Materials, systems and methods for optoelectronic devices

ABSTRACT

A photodetector is described along with corresponding materials, systems, and methods. The photodetector comprises an integrated circuit and at least two optically sensitive layers. A first optically sensitive layer is over at least a portion of the integrated circuit, and a second optically sensitive layer is over the first optically sensitive layer. Each optically sensitive layer is interposed between two electrodes. The two electrodes include a respective first electrode and a respective second electrode. The integrated circuit selectively applies a bias to the electrodes and reads signals from the optically sensitive layers. The signal is related to the number of photons received by the respective optically sensitive layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.13/209,264, filed Aug. 12, 2011, which is a Continuation of U.S.application Ser. No. 12/728,181, filed Mar. 19, 2010, now issued as U.S.Pat. No. 8,004,057, which is a Continuation of U.S. patent applicationSer. No. 12/106,256, filed Apr. 18, 2008, now issued as U.S. Pat. No.7,923,801, which claims the benefit of priority to all of the following:

(U.S.) Patent Application No. 60/912,581, filed Apr. 18, 2007;

U.S. Patent Application No. 60/958,846, filed Jul. 9, 2007;

U.S. Patent Application No. 60/970,211, filed Sep. 5, 2007;

U.S. Patent Application No. 61/026,440, filed Feb. 5, 2008;

U.S. Patent Application No. 61/026,650, filed Feb. 6, 2008;

U.S. Patent Application No. 61/028,481, filed Feb. 13, 2008; and

U.S. Patent Application No. 61/046,379, filed Apr. 18, 2008, all ofwhich are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present invention generally relates to optical and electronicdevices, systems and methods that include optically sensitive material,such as nanocrystals or other optically sensitive material, and methodsof making and using the devices and systems.

BACKGROUND

Optoelectronic device, such as image sensors and photovoltaic devices,may include optically sensitive material. Example image sensors includedevices that use silicon both for the sensing function and for theread-out electronics and multiplexing functions. In some image sensors,optically sensitive silicon photodiodes and electronics may be formed ona single silicon wafer. Other example image sensors may employ adistinct material, such as InGaAs (for short-wave IR sensing), oramorphous selenium (for x-ray sensing), for the sensing (photon toelectron conversion) function. Example photovoltaic devices includesolar cells that use crystalline silicon wafers for photon to electronconversion. Other example photovoltaic devices may use a separate layerof material such as amorphous silicon or polycrystalline silicon or adistinct material for photon to electron conversion. However, theseimage sensors and photovoltaic devices have been known to have a numberof limitations.

INCORPORATION BY REFERENCE

Each patent, patent application, and/or publication mentioned in thisspecification is herein incorporated by reference in its entirety to thesame extent as if each individual patent, patent application, and/orpublication was specifically and individually indicated to beincorporated by reference.

BRIEF DESCRIPTION OF FIGURES

The systems and methods described herein may be understood by referenceto the following figures:

FIG. 1 shows overall structure and areas according to an embodiment.

FIG. 2 a shows an example of a quantum dot 1200.

FIG. 2 b shows an array of quantum dots 1200.

FIG. 2 c shows colloidal quantum dots in an illustration taken from theWikipedia website. Ultraviolet light is incident on various sizes ofCadmium selenide (CdSe) quantum dots 1200, resulting in fluorescence.

FIG. 2 d shows various quantum dots 1200 arrayed in a quantum dotmaterial 200.

FIG. 2 e further illustrates the absorbance of colloidal quantum dotmaterial 200.

FIG. 3 is a side view of a portion of an embodiment of imagingconfigured in a lateral planar structure;

FIG. 3 a shows radiation entering pixel layouts.

FIG. 3 b shows an aspect of a closed simple geometrical arrangement ofpixels;

FIG. 3 c shows an aspect of a closed with interdigitation geometricalarrangement of pixels;

FIG. 3 d shows an aspect of a open simple geometrical arrangement ofpixels;

FIG. 3 e shows an aspect of an open with interdigitation geometricalarrangement of pixels;

FIG. 3 f shows a two-row by three-column sub-region within a generallylarger array of top-surface electrodes;

FIG. 3 g shows a quantum dot structure stack involving two separatelayers of quantum dot materials and a layer of dielectric materialbetween the two separate layers of quantum dot materials;

FIG. 3 h shows an example a multi-layered quantum dot structure withelectrical interconnections and pixel circuitry.

FIG. 3 i shows absorption and TEM graphs of small PbS nanocrystals. (a)Absorption of solution of as-synthesized oleic acid capped nanocrystalsand of solution of the nanocrystals after butylamine ligand exchange,the extended absorption into the infrared is due to loss of highconfinement followed by the formation of nanorods. (b) TEM of oleic acidcapped nanocrystals shows the synthesis of small nanocrystals withdiameter ˜3 nm. (c) After ligand exchange the nanocrystals conglomerateto form nanorods;

FIG. 3 j shows performance of the PbS small nanocrystal photodetector.(a) Spectral responsivity and normalized detectivity D* taken at 15 Hzof modulation frequency. The inset shows the noise equivalent power ofthe 0.0015 mm² detector in the visible range for modulation frequency of15 frames per second. The NEP of a typical silicon photodiode of similarsurface area is plotted for comparison. (b) Responsivity and noisecurrent density versus modulation frequency. (c) The detector exhibitsD*˜10¹³ Jones for modulation frequency up to 5 Hz whereas it has D*greater than 10¹² Jones up to 50 Hz at wavelength of 400 nm. The insetshows the resultant NEP of the detector at 400 nm with active area0.0015 mm² as a function of modulation frequency;

FIG. 3 k shows effects of the trap states on the photodetectorperformance. (a) Responsivity vs modulation frequency at variousillumination levels measured at optical wavelength of 632 nm. The longlived trap states dominate at low optical powers to provide with highphotoconductive gain. As higher power impinges on the detector theeffective traps are filled leading to decrease of the photoconductivegain and increase of the 3-dB bandwidth. The 3-dB bandwidth increasesfrom 8 Hz at low power to over 300 Hz at high optical power. Thisphenomenon could provide the detector with a self-limiting gainmechanism to avoid electronic saturation at high power levels. (b) Thephotocurrent versus optical illumination reveals a dynamic range of75-dB. The inset shows the responsivity as a function of opticalintensity. The responsivity drops beyond 10⁻⁵ W cm⁻² due to the fillingof the high gain trap states to enable the self-limiting mechanism ofgain. This measurement was taken with light at 830 nm.

FIG. 3 l shows spectral responsivity of the stacked device shown in theinset for dual-spectral detection. The small-quantum dot (QD) layerdetects effectively the short wavelength light, whereas the longerwavelengths are detected from the large-quantum dot (QD) layer. Theresponsivity of the large-quantum dot device before the stacking is alsoshown for comparison. The responsivities of the large-quantum dot devicein both cases have been normalized to their exciton peak value at 1230nm. The structure shown in the inset consists of gold electrodes withlength 3 mm, width 20 μm and height 100 nm. The spacing between theelectrodes is 20 μm and the applied bias was 100V.

FIG. 3 m shows the device structure. PbS quantum dots were spincoatedfrom solution on a pre-patterned interdigitated electrode. Theelectrodes were fabricated using standard photolithography on agold-coated F45 glass substrate—0.5 mm in thickness—from Schott. 10 nmof chromium were evaporated prior to 100 nm gold sputtering to achieveadhesion of gold to the glass substrate. The width of the gold stripesis 20 μm, the length is 3 mm and the spacing is 5 μm.

FIG. 3 n shows the dark current density as a function of the appliedfield of the reported device. The applied field is considered as theapplied voltage over the device width of 5 μm.

FIG. 3 o(a-f) shows scanning electron microscope (SEM) images of thesurface of a textured indium tin oxide (ITO) substrate beforenanocrystal deposition and the surface of a ITO substrate afternanocrystal deposition with and without the use of cross-linkingmolecules. a-b, Bare textured ITO substrate. c-d, textured ITO afternanocrystal deposition without cross-linker showing the exposed ITOwhich leads to short-circuited devices. Individual nanocrystals can beseen clustered in the crevices between sintered ITO particles. e-f,Surface of functional devices after nanocrystal deposition utilizingcross-linkers to obtain a continuous nanocrystal over-coating.

FIG. 3 p shows a table of the effects sintering treatment has on theperformance of photovoltaic devices. All measurements performed under 12mW/cm² 975 nm illumination

FIG. 3 q shows current-voltage curves of sintered device made withnanocrystals having a first excitonic transition at 1340 nm. The AM 1.5illumination intensity was 100 mW/cm². Monochromatic illuminationintensities of 12 and 70 mW/cm² were with 975 nm light.

FIG. 3 r shows external quantum efficiency of sintered devices. Insetshows schematic of band positions of the materials used in devices. PbSconduction and valence bands are drawn for 1 eV first excitonictransition nanocrystals by employing the effective mass approximation tomodify bulk energy levels.

FIG. 3 s is a stacked multilayer pixel having an electrode configurationwherein each respective first electrode (C1) is positioned laterally toat least a portion of the respective second electrode (c2), under anembodiment.

FIG. 3 t is a stacked multilayer pixel having an electrode configurationwherein one common electrode (CC) extends in the vertical direction overthe height of more than one of the photosensitive layers (QF1+QF2); andwherein separate, electrically independent, electrodes (C1 AND C2) areused to bias and collect current substantially independently from thephotosensitive layers (QF1 AND QF2), under an embodiment.

FIG. 3 u and FIG. 3 v is a side and top view, respectively, of a stackedmultilayer pixel having an electrode configuration wherein a commonelectrode (CC) is disposed around an electrode (C1) in electricalcontact with a first photosensitive layer (QF1); and the commonelectrode (CC) is disposed around an electrode (C2) in contact with asecond photosensitive layer (QF2), under an embodiment.

FIG. 3 w depicts an image sensor, in cross-section, showing byillustration how two layers of optically sensitive material, stackedatop one another, can be independently read out electrically;

FIG. 4 is a diagram illustrating a transient response to modulatedillumination at a 5V bias.

FIG. 5 a shows a Bayer filter pattern;

FIG. 5 b-f show examples of some alternative pixel layouts;

FIG. 5 g-l show pixels of different sizes, layouts and types used inpixel layouts;

FIG. 5 m shows pixel layouts with different shapes, such as hexagons;

FIG. 5 n shows pixel layouts with different shapes, such as triangles;

FIG. 5 o shows a quantum dot pixel, such as a multi-spectral quantum dotpixel or other pixel, provided in association with an optical element;

FIG. 5 p shows an example of a pixel layout;

FIG. 6 a illustrates the 3T transistor configuration for interfacingwith the quantum dot material;

FIG. 6 b; illustrates the 4T transistor configuration for interfacingwith the quantum dot material;

FIG. 6 c shows the noise equivalent exposure of a QD layer device ascompared with conventional Si CCD and CMOS sensor devices;

FIG. 7 a shows a quantum dot pixel 1800 structure according to an aspectof the present embodiment;

FIG. 7 b shows an example of an alternative (non-quantum dot)arrangement;

FIG. 7 c shows a focal plane array with a side view of an imaging systemwhich includes an integrated circuit with an array of electrodes locatedon the top surface thereof;

FIG. 7 d shows a side view of a portion of an optical device configuredin a vertical sandwich structure;

FIG. 7 e shows a side view of a portion of an optical device configuredin a lateral planar structure;

FIG. 7 f shows a plan view of a portion of an optical device configuredin a lateral interdigitated structure;

FIG. 8 shows an arrangement of quantum dot chip interconnections 2010.FIG. 20 shows an optical micrograph of a light sensitive layer formed onan electronic read-out chip;

FIG. 9 is an diagrammatic illustration of a scanning electron micrographof an integrated circuit in which an optically sensitive film;

FIG. 10 illustrates 4 process flows (a, b, c, and d) that may beemployed to produce integrated circuits similar to those described inFIG. 21;

FIG. 11 is a diagram of an alternative embodiment a scanning electronmicrograph of an integrated circuit in which an optically sensitivefilm;

FIGS. 12-19 illustrate a “standard” single pixel shutter arrangementaccording to an embodiment;

FIG. 20 a is a schematic diagram for a 16-to-2 shared pixel circuit;

FIG. 20 b is a layout for the 16-to-2 shared pixel circuit of FIG. 31 a;

FIG. 20 c shows a layout for pixel circuits for two pixel regions whereeach pixel circuit extends below both pixel regions;

FIGS. 21 a, 21 b, 22 a, 22 b, 23 a, 23 b, 24 a, 24 b, 25 a, 25 b, 26 a,26 b, 27 a, 27 b, 28 a, 28 b, 29 a, 29 b, 30 a, 30 b, 31 a, 31 b, 32 a,32 b, 33 a, 33 b, 34 a, 34 b, 35 a, 35 b, 36 a, and 36 b illustrate a“global” pixel shutter arrangement;

FIG. 37 shows the vertical profile of an embodiment where metalinterconnect layers of an integrated circuit shield the pixel circuitryon the semiconductor substrate from incident light;

FIG. 38 shows a layout (top view) of an embodiment where metalinterconnect layers of an integrated circuit shield the pixel circuitryon the semiconductor substrate from incident light;

FIG. 39 is a block diagram of functional blocks of a lateral pixelaccording to an embodiment;

FIG. 40 is a block diagram of functional blocks of a vertical pixelaccording to an embodiment;

FIGS. 41 through 45, 46 a, 46 b, 47, 48 a, 48 b, 49 a, 49 b, 50 a, 50 b,and 51 illustrate embodiments that include controlling temporal responseof photoconductive photodetectors via selective introduction of surfacetrap states;

FIGS. 52, 53/1, 53/2, and 54 through 66 illustrate an embodimentincluding fast, spectrally-tunable solution-processed photodetectors;

FIGS. 67/1, 67/2, 68/1, 68/2, and 69 illustrate an embodiment includingsmooth morphology ultrasensitive solution-processed photoconductors; and

FIG. 70 is a block diagram of an example system configuration that maybe used in combination with embodiments described herein.

Embodiments are described, by way of example only, with reference to theaccompanying drawings. The drawings are not necessarily to scale. Forclarity and conciseness, certain features of the embodiment may beexaggerated and shown in schematic form.

DETAILED DESCRIPTION

Image sensors incorporate arrays of photodetectors. These photodetectorssense light, converting it from an optical to an electronic signal. Itis often desired that such photodetectors possess the followingfeatures, individually or in combination(s):

be readily integrable with other circuitry related to the image sensingfunction, such as circuits which store charge, circuits which relaysignal levels to the periphery of the array, circuits which manipulatethese signal levels in the analog domain, circuits which convert analoginto digital signals, and circuits which process image-related data inthe digital domain.

provide a maximum of sensitivity to light within the wavelength band, orbands, of interest. Sensitivity is often quantified using the measuresignal-to-noise (SNR) at a given level of illumination. Signal ismaximized when the responsivity, quantum efficiency, or gain of thedevice is maximized. Noise is minimized when random fluctuations inelectronic signals are minimized, subject to the limits prescribed bynatural fluctuations in electrical currents and voltages at a giventemperature. Relatedly, noise and other uncontrolled ordifficult-to-predict variations in background signal are generallyminimized when the magnitude of dark current is minimized. For this andother reasons, photodetectors having high sensitivity and low darkcurrent are desired.

provide a response in time that is suitably fast. Applications such asvideo imaging and shutterless still-image acquisition typically requirephotodetectors whose signal levels change substantially completely inresponse to a transient within fewer than 100 milliseconds (10 framesper second), or fewer than 33 milliseconds (30 frames per second), oreven 1 millisecond ( 1/1000 second exposure of a still image).

provide for the detection of a wide range of light intensities in amanner that can conveniently be processed by available electroniccircuitry. This feature is known as providing high dynamic range. Onemeans of providing high dynamic range is to compress the measuredelectronic response as a function of the incident optical stimulus. Suchcompression may be referred to as a sublinear, i.e. a nonlinear withdecreasing slope, dependence of electrical signal on incident intensity.High dynamic range may also be facilitated by employing a photodetectorwhose gain may be controlled, such as through the selection of a voltagebias known to produce a specific gain.

provide for the convenient discrimination among different spectral bandsof electromagnetic radiation. Of particular interest are the x-ray,ultraviolet, visible (including blue, green, and red), near-infrared,and short-wavelength infrared bands.

Herein are discussed means of creating, integrating with circuits, andexploiting in a variety of applications photodetectors, and arrays ofphotodetectors, that possess many of these properties in combination.Specifically:

the photodetectors described herein can readily be integrated with otherportions of the image sensor circuit and system by straightforward,low-cost methods such as spin-coating, spray-coating, drop-coating, andself-assembly. Embodiments include exchanging ligands passivatingnanoparticle surfaces for shorter ligands that will provide forappropriate charge carrier mobilities once films are formed. Embodimentsinclude solution-phase exchanges which enable the realization ofsmooth-morphology films necessary to the realization of image sensorshaving acceptable consistent dark currents and photoresponses across anarray.

The photodetectors described herein provide a maximum of sensitivitythrough a combination of means. They maximize signal by providingphotoconductive gain. Typical values for photoconductive gain range from1-10, resulting in responsivities in, for example, the visiblewavelengths ranging from 0.4 A/W to 4 A/W. In embodiments, thephotodetectors described herein minimize noise by fusing nanocrystalcores such as to ensure substantially non-noise-degrading electricalcommunication among the particles making up the optically sensitivelayer through which current flows. In embodiments, the photodetectorsdescribed herein minimize dark current by minimizing the net doping ofthe active layer, thus ensuring that the dark carrier density, and thusthe dark conductance, of these optically sensitive materials isminimized. In embodiments, the photodetectors described herein minimizedark current by providing an electrode-to-nanocrystalline-layerelectrical connection that blocks typically one type of carrier,including potentially the majority carrier at equilibrium. Inembodiments, cross-linking molecules are employed that utilize chemicalfunctionalities that remove oxides, sulfates, and/or hydroxidesresponsible for p-type doping. Thus, in embodiments, a more intrinsic oreven n-type optically sensitive layer may be provided, leading tolowered dark currents. In embodiments, many steps in quantum dotsynthesis and/or processing and/or device packaging may be performed ina controlled environment such as a Schlenk line or Glove Box; andoptically sensitive layers may be encapsulated using substantiallyimpermeable layers such as oxides, oxynitrides, or polymers such asparylene, or epoxies, in order to prevent reactive gases such as oxygenor water from significantly permeating the optically sensitive layer. Inthis manner, desired combinations of properties such as gain, darkcurrent, and lag may be preserved over the desired useful lifetime of animage sensor.

The photodetectors described herein provide a time-domain response thatcan be as rapid as sub-100-milliseconds, sub-30-milliseconds, andsub-1-millisecond. In embodiments, this is achieved by providinggain-providing (and persistence-providing) trap states associated withthe optically sensitive layer that trap at least one type of carrier foronly a limited time period such as 100 milliseconds, 30 milliseconds, or1 millisecond. In embodiments, PbS nanoparticles are decorated withPbSO3, an oxide of PbS, which is shown to have a trap state lifetime inthe vicinity of 20-30 milliseconds, providing for a transient responsesuited to many video imaging applications. In embodiments, photodiodesare instead provided based on colloidal quantum dot layers, wherein twoelectrical contacts having appreciably different work functions areemployed to contact the active layer. In embodiments, dark currents maybe minimized through operation of such devices without the applicationof an appreciable external voltage bias. In embodiments, cross-linkingmoieties such as benzenedithiol, a bidentate linker, may be employed toremove and/or passivate certain trap states that may be present, or maydevelop, in such materials.

The photodetectors described herein provide a means of enhancing dynamicrange by producing a sublinear dependence of electrical signal (such asphotocurrent). Over a region of low to middling intensities, trap statesare available to become filled, and escape occurs following somemoderate persistence, or trap state, lifetime, such as 30 millisecondsfor example. At higher intensities, these trap states becomesubstantially filled, such that charge carriers experience shorterlifetimes, or persistence times, corresponding to lower differentialgains. As a result these devices exhibit substantially constant gainsover a range of low to middling intensities, followed by a gentleroll-off in gain at higher intensities. Put another way, at low tomiddling intensities, photocurrent depends approximately linearly onintensity, but at higher intensities, photocurrent exhibits sublineardependence on intensity. In embodiments, photodetectors are providedwherein photoconductive gain depends on the bias applied to a device.This arises because gain is proportional to carrier lifetime divided bycarrier transit time, and transit time varies in inverse proportionalitywith applied field. In embodiments, circuits are developed that exploitthis dependence of gain on bias to increase dynamic range.

In embodiments, photodetectors described herein may readily be altered,or ‘tuned’, to provide sensitivity to different spectral bands. Onemeans of tuning is provided through the quantum size effect, wherebynanoparticle diameter is decreased, in cases through synthetic control,to increase the effective bandgap for the resulting quantum dots.Another means of tuning is provided through the choice of materialscomposition, wherein the use of a material having a larger bulk bandgapgenerally facilitates the realization of a photodetector withresponsivity onset at a higher photon energy. In embodiments,photodetectors having different absorption onsets may be superimposed toform vertical pixels, wherein pixel(s) closer to the source of opticalsignal absorb and sense higher-energy bands of electromagneticradiation, whereas pixel(s) further from the source of optical signalabsorb and sense lower-energy bands.

FIG. 1 shows structure of and areas relating to quantum dot pixel chipstructures (QDPCs) 100, according to example embodiments. As illustratedin FIG. 1, the QDPC 100 may be adapted as a radiation 1000 receiverwhere quantum dot structures 1100 are presented to receive the radiation1000, such as light. The QDPC 100 includes, as will be described in moredetail herein, quantum dot pixels 1800 and a chip 2000 where the chip isadapted to process electrical signals received from the quantum dotpixel 1800. The quantum dot pixel 1800 includes the quantum dotstructures 1100 include several components and sub components such asquantum dots 1200, quantum dot materials 200 and particularconfigurations or quantum dot layouts 300 related to the dots 1200 andmaterials 200. The quantum dot structures 1100 may be used to createphotodetector structures 1400 where the quantum dot structures areassociated with electrical interconnections 1404. The electricalconnections 1404 are provided to receive electric signals from thequantum dot structures and communicate the electric signals on to pixelcircuitry 1700 associated with pixel structures 1500. Just as thequantum dot structures 1100 may be laid out in various patterns, bothplanar and vertical, the photodetector structures 1400 may haveparticular photodetector geometric layouts 1402. The photodetectorstructures 1400 may be associated with pixel structures 1500 where theelectrical interconnections 1404 of the photodetector structures areelectrically associated with pixel circuitry 1700. The pixel structures1500 may also be laid out in pixel layouts 1600 including vertical andplanar layouts on a chip 2000 and the pixel circuitry 1700 may beassociated with other components 1900, including memory for example. Thepixel circuitry 1700 may include passive and active components forprocessing of signals at the pixel 1800 level. The pixel 1800 isassociated both mechanically and electrically with the chip 2000. Froman electrical viewpoint, the pixel circuitry 1700 may be incommunication with other electronics (e.g. chip processor 2008). Theother electronics may be adapted to process digital signals, analogsignals, mixed signals and the like and it may be adapted to process andmanipulate the signals received from the pixel circuitry 1700. In otherembodiments, a chip processor 2008 or other electronics may be includedon the same semiconductor substrate as the QDPCs and may be structuredusing a system-on-chip architecture. The chip 2000 also includesphysical structures 2002 and other functional components 2004, whichwill also be described in more detail below.

The QDPC 100 may be manufactured using a number of manufacturingprocesses 300 such as quantum dot solution processing 400, quantum dotmaterials processing 500, photodetector processing 600, pixel processing700, pixel/chip processing 800, overall system integrations 900, andother such processes. The QDPC 100 may also be incorporated intointegrated systems 2200 where the integrated systems 2200 may bestructured 2202 and have various features 2204. The structures 2202 andfeatures 2204 may be adapted to serve particular applications and/ormarkets 2100. An integrated product may include conventional pixelstructures (e.g. CCD or CMOS) along with quantum dot pixel structures1800 in certain embodiments.

The photoconductive layer of the QDPC may have a resistance that changesin response to changes in radiation 1000. In embodiments, the QDPC is animage detector that monolithically sits on top of a semiconductor. Thephotoconductive coating (e.g. quantum dot material 200) may betransferred (e.g. spin coated) on top of the integrated circuit. Aphoton generates an electron-hole pair. The hole can participate inconduction. An electron is trapped for a trap time ranging fromnanoseconds to microseconds to milliseconds depending on the nature ofthe traps. The hole is transported during a period on the order ofmicroseconds. The increase in conductivity thus persists over manymultiples of the transit time for the hole across the devices. As aresult, multiple charges are, over the measurement interval, measured inan external circuit for a given absorbed photon. In an alternativeembodiment, the electron is transported, with the increase inconductivity persisting over many multiples of the transit time for theelectron across the device. In some embodiments, the QDPC is a generallylinear device, which can benefit from a change in resistance for anextended period, generally ranging, on an order of magnitude, from onemicrosecond to one second with desirable periods in the range ofapproximately 100 microseconds to approximately one millisecond. Inother embodiments, the current across the quantum dot material 200 has anon-linear relationship to the intensity of light absorbed by theoptically sensitive layer of quantum dot material 200. In someembodiments, analog or digital circuitry on the chip 2000 or on anotherchip associated with the QDPC may be used to linearize the signals readfrom the pixel regions in order to produce digital pixel data that canbe used by a digital camera or other system in which the QDPC is used.Embodiments described herein relate to measuring the persistentresistance change associated with the photoconductive layer. Certain ofthese embodiments involve low cost, largest dynamic range, mostefficient, least noisy, etc. methods by which to measure thisresistance. In some embodiments, the QDPC 100 consists of aphotoconductive material contacted by at least two generally differentcontacts. Either of these contacts may be ohmic, or may form a Schottkycontact. Upon absorption of a photon, an electron-hole pair is created.This may contribute to the photoconductive gain described above. Inaddition, both the electron and the hole may be electrically transportedto some degree, either under an applied or no applied external bias. Theelectron and the hole may be transported, with generally differentefficiencies, to their respective contacts, depending on the biasing ofthe device. The device may exhibit a generally nonlinear relationshipbetween current and voltage in some embodiments. In certain biasingregimes it may produce photoconductive gain, and in other regimes thesame device may not. In certain biasing regimes the device may producemuch lower dark currents than in others. In some embodiments, there areregimes of significant photoconductive gain (e.g. 1, 10, or 100) butwith low dark current (e.g. 1 nA/cm2, or 1 uA/cm2).

Radiation 1000

The QDPC 100 detects electromagnetic radiation 1000, which inembodiments may be any frequency of radiation from the electromagneticspectrum. Although the electromagnetic spectrum is continuous, it iscommon to refer to ranges of frequencies as bands within the entireelectromagnetic spectrum, such as the radio band, microwave band,infrared band (IR), visible band (VIS), ultraviolet band (UV), X-rays,gamma rays, and the like. The QDPC 100 may be capable of sensing anyfrequency within the entire electromagnetic spectrum; however,embodiments herein may reference certain bands or combinations of bandswithin the electromagnetic spectrum. It should be understood that theuse of these bands in discussion is not meant to limit the range offrequencies that the QDPC 100 may sense, and are only used as examples.Additionally, some bands have common usage sub-bands, such as nearinfrared (NIR) and far infrared (FIR), and the use of the broader bandterm, such as IR, is not meant to limit the QDPCs 100 sensitivity to anyband or sub-band. Additionally, in the following description, terms suchas “electromagnetic radiation”, “radiation”, “electromagnetic spectrum”,“spectrum”, “radiation spectrum”, and the like are used interchangeably,and the term color is used to depict a select band of radiation 1000that could be within any portion of the radiation 1000 spectrum, and isnot meant to be limited to any specific range of radiation 1000 such asin visible ‘color’.

Quantum Dot 1200

A quantum dot 1200 may be a nanostructure, typically a semiconductornanostructure, that confines a conduction band electrons, valence bandholes, or excitons (bound pairs of conduction band electrons and valenceband holes) in all three spatial directions. The confinement can be dueto electrostatic potentials (e.g., generated by external electrodes,doping, strain, impurities), the presence of an interface betweendifferent semiconductor materials (e.g., in core-shell nanocrystalsystems) or a semiconductor and another material (e.g., a semiconductordecorated by organic ligands; or by a dielectric such as an oxide suchas PbO, a sulfite such as PbSO3, a sulfate such as PbSO4, or SiO2), thepresence of a semiconductor surface, or a combination of one or more ofthese. A quantum dot exhibits in its absorption spectrum the effects ofthe discrete quantized energy spectrum of an idealized zero-dimensionalsystem. The wave functions that correspond to this discrete energyspectrum are typically substantially spatially localized within thequantum dot, but extend over many periods of the crystal lattice of thematerial.

FIG. 2 a shows an example of a quantum dot 1200. In one exampleembodiment, the QD 1200 has a core 1220 of a semiconductor or compoundsemiconductor material, such as PbS. Ligands 1225 may be attached tosome or all of the outer surface or may be removed in some embodimentsas described further below. In some embodiments, the cores 1220 ofadjacent QDs may be fused together to form a continuous film ofnanocrystal material with nanoscale features. In other embodiments,cores may be connected to one another by linker molecules. In someembodiments, trap states may be formed on the outer surface of thenanocrystal material. In some example embodiments, the core may be PbSand trap states may be formed by an oxide such as PbSO3 formed on theouter surface of core 1220.

FIG. 2 b shows a two-dimensional representation of a portion of a QDlayer. The layer includes a continuous network of fused QD cores 1220,having outer surfaces 1221 that are of a different composition than thatin the core, e.g., oxidized core material such as PbSO3, or a differentkind of semiconductor. The individual QD cores in the film are inintimate contact, but continue to exhibit many of the properties ofindividual quantum dots. For example, a lone (unfused) quantum dot has awell-characterized excitonic absorbance wavelength peak that arises fromquantum effects related to its size, e.g., 1-10 nm. The excitonicabsorbance wavelength peak of the fused QDs in the film is notsignificantly shifted from the central absorbance wavelength the waspresent prior to fusing. For example, the central absorbance wavelengthmay change by about 10% or less when fused. Thus, the QDs in the filmretain their quantum effects, despite the fact that they may be anintegral part of a macroscopic structure.

Current is not generally thought of as “flowing” through a lone (unfusedand unlinked) QD; instead, electrons simply occupy well-known quantumenergy states in the quantum dot core. If two lone (unfused) QDs arebrought near each other, current can flow between them by electron orhole hopping between the QDs. Current more readily flows between fusedQD cores, even though the cores themselves generally retain theirquantum energy states. Because the cores are in contact, electrons canmore easily move between them. It may also be said that thewavefunctions of the quantum-confined electron or hole states inadjacent dots see increased overlap as the quantum dots are broughtclose together to form a fused quantum dot-based solid, while at thesame time not fusing the QDs to such an extent that they lose their“identity,” namely their individual characteristics that provide quantumconfinement, in turn resulting in their excitonic feature manifest intheir absorption spectrum. In embodiments, mobilities may range from10⁻⁷ cm²/Vs to 10² cm²/Vs. It is also possible to “overfuse” QDs, inwhich case they no longer exhibit many of the normal properties ofindividual quantum dots. In the overfused case, the cores of the QDs donot generally have their own quantum energy levels, but the energylevels are instead distributed over multiple QD cores. This results in afilm with a very low electrical resistance, but which in many ways iseffectively a bulk semiconductor material. “Overfused” QDs can also berecognized experimentally by their relatively large shift (e.g., greaterthan about 10%) to the red (longer wavelengths) in their absorptionand/or emission spectra. Complete fusing, and complete loss of quantumconfinement properties, may be recognized when the solid approachestaking on the absorption spectral characteristics of a bulk material,e.g. absorption begins near the bulk materials' bandgap.

In some embodiments, QD cores are linked by linker molecules asdescribed further below. This allows current to flow more readily thanthrough unlinked, unfused QDs. However, the use of linker molecules toform a continuous film of QDs instead of fusing the cores may reduce thedark current for some photoconductor and image sensor embodiments.

In certain embodiments the QD layer is exceptionally radiation 1000sensitive. This sensitivity is particularly useful for low-radiation1000 imaging applications. At the same time, the gain of the device canbe dynamically adjusted so that the QDPC saturates, that is, additionalphotons continue to provide additional useful information that can bediscerned by the read-out electronic circuit. Tuning of gain can beconveniently achieved by changing the voltage bias, and thus theresultant electric field, across a given device, e.g., a pixel. Asdiscussed in greater detail below, photoconductive photovoltaic gain,and correspondingly the responsivity in A/W, can be made to varyapproximately linearly with bias and field. Thus, in a given device, abias of about 1 V may result in a gain of about 10, while a bias ofabout 10 V may result in a gain of about 100.

Some embodiments of QD devices include a QD layer and a custom-designedor pre-fabricated electronic read-out integrated circuit. The QD layeris then formed directly onto the custom-designed or pre-fabricatedelectronic read-out integrated circuit. The QD layer may additionally bepatterned so that it forms individual islands. In some embodiments,wherever the QD layer overlies the circuit, it continuously overlaps andcontacts at least some of the features of the circuit. In someembodiments, if the QD layer overlies three-dimensional features of thecircuit, the QD layer may conform to these features. In other words,there exists a substantially contiguous interface between the QD layerand the underlying electronic read-out integrated circuit. One or moreelectrodes in the circuit contact the QD layer and are capable ofrelaying information about the QD layer, e.g., an electronic signalrelated to the amount of radiation 1000 on the QD layer, to a readoutcircuit. The QD layer can be provided in a continuous manner to coverthe entire underlying circuit, such as a readout circuit, or patterned.If the QD layer is provided in a continuous manner, the fill factor canapproach about 100%, with patterning, the fill factor is reduced, butcan still be much greater than a typical 35% for some example CMOSsensors that use silicon photodiodes.

In many embodiments, the QD optical devices are readily fabricated usingtechniques available in a facility normally used to make conventionalCMOS devices. For example, a layer of QDs can be solution-coated onto apre-fabricated electronic read-out circuit using, e.g., spin-coating,which is a standard CMOS process, and optionally further processed withother CMOS-compatible techniques to provide the final QD layer for usein the device. Details of QD deposition and further processing areprovided below. Because the QD layer need not require exotic ordifficult techniques to fabricate, but can instead be made usingstandard CMOS processes, the QD optical devices can be made in highvolumes, and with no significant increase in capital cost (other thanmaterials) over current CMOS process steps.

FIG. 2 e further illustrates the absorbance of some example colloidalquantum dot materials 200.

Example nanocrystal materials that may be used as optically sensitivelayers of QDs in example embodiments are described further below as wellas methods for making the same, including those with fused or linkedcores and trap states. These nanocrystal materials can be used toprovide QD layers with photoconductive in example embodiments. Exampleembodiments of the QDPC 100 shown in FIG. 1 may use any of thesenanocrystal materials as an optically sensitive layer to form a pixelregion of a photosensor array. These nanocrystal materials may also beused to form the optically sensitive layer in embodiments of the otherexample image sensors, pixel regions and photoconductors described inthis specification. In particular embodiments, the optically sensitivelayer of the pixel regions is formed from compound semiconductornanocrystal cores, such as PbS or other materials described below, thatare fused or linked and oxides of the core material, such as PbSO3, areformed on the outer surface to form trap states to providephotoconductive gain. These are examples only and other QDs or opticallysensitive layers may be used in the pixel regions in other embodiments.In some embodiments, other optically sensitive layers such as siliconphotodiodes may be used in combination with or instead of QDs for pixelregions or for particular layers in pixel regions.

Quantum Dot Structures 1100

An aspect of the example embodiment in FIG. 1 relates to quantum dotstructures 1100. Quantum dot structures 1100 generally include quantumdots 1200, quantum dot materials 200 and quantum dot layouts 1300.

Example embodiments provide quantum dot (QD) 1200 devices and methods ofmaking nanoscale crystalline material devices. Many embodiments areoptical devices that possess enhanced gain and sensitivity, and whichcan be used in optical, including radiation 1000 imaging applications,photovoltaic applications, among other applications. The term “quantumdot” or “QD” is used interchangeably herein with the term “nanocrystal,”and it should be understood that the present embodiments are not limitedexclusively to standalone quantum dots but rather to any nanoscalecrystalline material, including continuous films having nanoscalefeatures, such as those formed by networks of fused or linkednanocrystal cores.

The term ‘nanocrystal film’ is used to describe a material that includescrystalline components that can typically range in size from 0.5 nm to10 nm, and wherein the constituent nanocrystals' axes of symmetry (or ofperiodicity) in their repetition of atoms is, in generally, notwell-ordered across the film, i.e. from nanocrystal to nanocrystal. Theterm ‘colloidal quantum dot film’ is used to describe nanocrystallinefilms wherein the constituent nanocrystals are approximately same-sized,such as a film in which the nanocrystals are on average 2 nm and have astandard deviation in diameter of less than 0.5 nm. There exists anothercategory of quantum dots, known as epitaxial, orStranski-Krastanow-grown quantum dots, that are not encompassed in theterm ‘nanocrystal film or ‘colloidal quantum dot film’ as definedherein. Epitaxial quantum dot solids are generally lattice-matched, andthus the constituent crystals possess approximately the same latticeorientation as one another.

Some embodiments of the QD optical devices are single image sensor chipsthat have a plurality of pixels, each of which includes a QD layer thatis radiation 1000 sensitive, e.g., optically active, and at least twoelectrodes in electrical communication with the QD layer. The currentand/or voltage between the electrodes is related to the amount ofradiation 1000 received by the QD layer. Specifically, photons absorbedby the QD layer generate electron-hole pairs, such that, if anelectrical bias is applied, a current flows. By determining the currentand/or voltage for each pixel, the image across the chip can bereconstructed. The image sensor chips have a high sensitivity, which canbe beneficial in low-radiation-detecting 1000 applications; a widedynamic range allowing for excellent image detail; and a small pixelsize. The responsivity of the sensor chips to different opticalwavelengths is also tunable by changing the size of the QDs in thedevice, by taking advantage of the quantum size effects in QDs. Thepixels can be made as small as 1 square micron or less, or as large as30 by 30 microns or more or any range subsumed therein.

In many embodiments, the optically sensitive QD layer includes aplurality of QDs that have been specially processed to give the layer anenhanced gain and sensitivity. Specifically, a plurality of QDs may befabricated using the methods described below, and in some embodimentsmay include a core as well as an outer surface that includes a pluralityof ligands. The ligands may be exchanged for shorter ligands, in certaincases volatile ligands, and then the ligand-exchanged QDs aresolution-deposited onto a substrate to form a QD precursor layer in someembodiments. Other methods for forming and/or depositing nanocrystalmaterials may also be used as described below. The substrate itself mayinclude one or more electrodes, or the electrodes may be deposited in alater step. Subsequently, the short ligands are removed from the QDprecursor layer in some embodiments. This may bring the QDs in the QDprecursor layer into very close proximity. In embodiments, at least someof the QDs may make contact with their neighbors. This contact betweenQDs may be referred to as “necking”. Bringing the nanoparticles closertogether may produce an increased ease of movement of electrons and/orholes between nanoparticles, thus improving the mobility for chargecarries traversing the electrical path within the layer.

In some embodiments, necked QDs may be annealed, which may fuse thenecked QDs together. In this instance, the QD precursor layer may bemaintained in an inert atmosphere after ligand removal, so that theouter surfaces of the individual QDs do not oxidize until annealing iscomplete. While two given fused QDs in the annealed QD layer retain alarge portion of their original shape, and thus remain individuallyrecognizable, after annealing the QDs may no longer be physicallydistinct from each other. Instead, the cores of the QDs together mayform a continuous electrical path, which may thus further improve theconductivity of the electrical path within the layer. Thus, if manyadjacent QDs neck, or fuse together into an annealed QD layer, they mayform an electrical pathway with a physical extent that is substantiallygreater than that of the individual QDs, and through which current willreadily flow. In some embodiments, a QD film may have a macroscopicextent, though the QDs themselves are nanoscopic. In some embodiments,the finished QD layer may essentially be considered a continuousinorganic film having nanoscale features. The general shapes of theindividual QDs may still be recognizable, but their cores form acontinuous electrical pathway that is mechanically robust. For example,a micrograph of the finished QD layer would show the general shape andsize of the individual QDs from which the layer is formed, as well asrobust joints between many adjacent QDs. In some embodiments, thenanocrystal cores may be linked by other molecules rather than fusedtogether.

In many embodiments, the fused QD layer is subsequently processed tomodify its outer surfaces. For example, a material such as asemiconductor shell can be coated on the outer surfaces of the fusedquantum dots. Or, for example, defect states can be formed on theexposed outer surfaces of the QDs, e.g., by oxidizing the fused QDslayer. These defect states effectively trap electrons excited byphotons, so that they recombine with holes far less readily and thusgreatly enhance the amount of current that a given photon generates inthe finished QD layer. This greatly enhances the photoconductive gain ofthe device. The fused QD cores, and the juncture between them, willgenerally not have defect states, so current will flow readily betweenthem, in certain embodiments. Photoconductive gain occurs because thepersistence of the trap state is longer than the transit time ofcarriers across the layer of nanocrystal material.

Photodetector Structures 1400

An aspect of the example embodiment in FIG. 1 relates to photodetectorstructures 1400. Photodetector structures 1400 generally includeelectrical connections 1404 that are connected to the quantum dotstructures 1100 and adapted to carry an electric signal or charge fromthe quantum dot structures 1100 to be communicated to associated pixelcircuitry 1700. The electrical interconnections 1404 may be laid out ina photodetector geometric layout 1402 that corresponds with a quantumdot layout 1300 as described herein. For example, if the quantum dotlayout is a closed interdigitated pattern 1438 then the layout of theelectrical interconnections may be laid out in a similar pattern suchthat the electrical charge or signal from the nodes can be transferredfrom the dots to the pixel circuitry 1700. In other embodiments, theelectrical interconnections may be laid out in a particular pattern andthe quantum dot structures 1100 may be laid out in another pattern (e.g.dispersed in a continuous film) such that the electricalinterconnections 1404 draw charge or signal from only a portion of thequantum dot structure 1100.

In embodiments the photodetector structure includes a semiconductor filmcontacted with some number of electrodes. While many of the embodimentsdisclosed herein describe the use of photodetectors structures withimage detection systems, it should be understood that the photodetectormay be a photodiode (e.g., photovoltaic with gain or no gain) or aphotoconductor in some embodiments. The photoconductor may generallypass holes and stop or fail to pass electrons. Some of the energeticrelationships include Fermi energy, work function, valence energy, andconduction band edge. Photodetector structures 1400 may contain materialcombinations such as including or containing two or more types ofquantum dots. In some example embodiments, the photodetector structuresmay form a unipolar device in which the transport of one carrier type(electrons or holes) predominates over the transport of the other type(holes or electrons). For example, in PbS photoconductive colloidalquantum dot detectors described herein, holes may be the flowing carrierand may have a mobility of at least 10× greater than electrons. Forexample, the hole mobility may equal 1E-4 cm2/Vs while the electronmobility may be inferior to 1E-5 cm2/Vs.

The photodetector structure 1400 is a device configured so that it canbe used to detect radiation 1000 in example embodiments. The detectormay be ‘tuned’ to detect prescribed wavelengths of radiation 1000through the types of quantum dot structures 1100 that are used in thephotodetector structure 1400. The photodetector structure can bedescribed as a quantum dot structure 1100 with an I/O for someinput/output ability imposed to access the quantum dot structures' 1100state. Once the state can be read, the state can be communicated topixel circuitry 1700 through an electrical interconnection 1404, whereinthe pixel circuitry may include electronics (e.g., passive and/oractive) to read the state. In an embodiment, the photodetector structure1400 may be a quantum dot structure 1100 (e.g., film) plus electricalcontact pads so the pads can be associated with electronics to read thestate of the associated quantum dot structure 1100. In an embodiment,the electrical interconnections 1404 may include a KDP electric fielddetector or other field detection system. Once an electrical connectionis made with the quantum dot structure and made available, it may beread through contact (e.g. charge, voltage, current, power, resistance)or non-contact (e.g. magnetic field, electric field, capacitance,inductance) measurement methods.

In embodiments, the photodetector structure 1400 may include multiplelayers of quantum dot material 200, spin-coated on top of one another.There may be insulating materials laid down between these layers inorder to reduce crosstalk between the layers. In embodiments, thismaterial may be a very thin dielectric material, with a thickness of1000 angstroms for instance. The application of this dielectric mayinvolve process steps to assure that the dielectric does not interferewith the electrical contacts intended to connect with the layers ofquantum dot material 200, such as by masking off or removal from theelectrical connections. For instance, removal may involve an etchingprocess. In embodiment, the dielectric may be laid down vertically toavoid making contact with the top of the electrodes.

In an embodiment, post-processing may involve sensitization of aphotodetector 1400 by a combination of illumination and temperature. Thephotodetector 1400 sensitivity may freeze in place as long as there isuniform illumination; all other parameters may reach an equilibriumvalue. For example, a photodetector 1400 may be sensitized by heating toa temperature for a period of time. A combination of time andtemperature may affect the sensitivity. Power from the photodetector1400 may be dissipated on a pixel-by-pixel basis. Power may be inverselyproportional to the response. Dissipation may normalize the response.Post-processing may involve illumination with a flat field that resultsin a consistent photodetector response across an array. Theself-flattening may involve uniform illumination of the whole sensor: ifthere were pixels not having the desired level of gain, the uniformillumination will serve to increase their gain. Large currents may gothrough “hot” pixels, which may diminish their response. If the sensoris exposed to a uniform optical field, it may anneal to a flat response.

The quantum dot structures 1100 may also have planar layouts in someembodiments. The planar layouts may be provided to increase thesensitivity of a QDPC to a certain wavelength or range of wavelengthsfor example. Patterns of quantum dot structures in the horizontal planemay be provided for a number of reasons including, for example,increasing the sensitivity to a wavelength, decreasing the sensitivityto a wavelength, and compensating for the absorption, refraction,reflection or other properties associated with the materials.

In embodiments, a charge region is produced in the quantum dot structure1100 such that charges produced in the charge region as a result ofincident radiation 1000 are isolated from those associated with adjacentcharge regions, and the effect of illumination only over the region ofinterest can be measured. This method can be used to create a map ofcharge response areas that define the pixels or portions of the pixels.For example, within a layer of quantum dot structure 1100 it may bedesired to define areas (e.g., millions of areas) that may be used asseparate pixel portions. A matrix or set of positively biased electrodesand ground plane or negatively charged electrodes may be associated withthe layer (e.g. through a set or matrix of electrical interconnects).When radiation 1000 to which the layer is responsive falls on the subportion of the layer a charge in a corresponding area develops and ismoved towards the positively biased electrode in the area. By monitoringthe electrodes the area of activity can be identified, and the intensitycan be measured and associated with a particular pixel or group ofpixels. Several planar electrical interconnection patterns areillustrated in FIGS. 3 b-3 e including examples of such patterns. Eachof the patterns presented in FIGS. 3 b-3 e illustrates a positivelybiased electrical interconnection 1452 and a ground or negatively biasedinterconnection 1450 as an example of how such an arrangement mayoperate, but other configurations and biases may be used in otherembodiments.

FIG. 3 b represents closed-simple patterns 1430 (e.g., conceptualillustration) and 1432 (e.g., vias used to create photodetectorstructures). In the closed-simple illustrations 1430-1432 the positivelybiased electrical interconnect 1452 is provided in the center area of agrounded contained square electrical interconnect 1450. Squareelectrical interconnect 1450 may be grounded or may be at anotherreference potential to provide a bias across the optically sensitivematerial in the pixel region. For example, interconnect 1452 may bebiased with a positive voltage and interconnect may be biased with anegative voltage to provide a desired voltage drop across a nanocrystalmaterial in the pixel region between the electrodes. In thisconfiguration, when radiation 1000 to which the layer is responsivefalls within the square area a charge is developed and the charge isattracted to and move towards the center positively biased electricalinterconnect 1452. If these closed-simple patterns are replicated overan area of the layer, each closed simple pattern forms a portion or awhole pixel where they capture charge associated with incident radiation1000 that falls on the internal square area. In example embodiments, theelectrical interconnect 1450 may be part of a grid that forms a commonelectrode for an array of pixel regions. Each side of the interconnect1450 may be shared with the adjacent pixel region to form part of theelectrical interconnect around the adjacent pixel. In this embodiment,the voltage on this electrode may be the same for all of the pixelregions (or for sets of adjacent pixel regions) whereas the voltage onthe interconnect 1452 varies over an integration period of time based onthe light intensity absorbed by the optically sensitive material in thepixel region and can be read out to generate a pixel signal for eachpixel region. In example embodiments, interconnect 1450 may form aboundary around the electrical interconnect 1452 for each pixel region.The common electrode may be formed on the same layer as interconnect1452 and be positioned laterally around the interconnect 1450. In someembodiments, the grid may be formed above or below the layer ofoptically sensitive material in the pixel region, but the bias on theelectrode may still provide a boundary condition around the pixel regionto reduce cross over with adjacent pixel regions.

FIG. 3 c illustrates closed patterns of electrical interconnections withinterdigitation 1434 (e.g., conceptual illustration) and 1438 (e.g.,vias used to create photodetector structures). The interdigitationcreates a pattern where the electrical interconnections are intertwinedin some manner. Similar to the closed-simple patterns, these closedpatterns may be used to capture charge within the confines of the outergrounded electrical interconnect 1450 and move the charges to thepositively biased electrical interconnect 1452. As with FIG. 3 b, outerelectrical interconnect 1450 may be grounded or be at some otherreference potential and may form a common electrode around an array ofpixels or set of adjacent pixels.

FIG. 3 d illustrates open simple patterns of electrical interconnects.The open simple patterns do not, generally, form a closed pattern. Theopen simple pattern does not enclose a charge that is produced as theresult of incident radiation 1000 with the area between the positivelybiased electrical interconnect 1452 and the ground 1450; however, chargedeveloped within the area between the two electrical interconnects willbe attracted and move to the positively biased electrical interconnect1452. An array including separated open simple structures may provide acharge isolation system that may be used to identify a position ofincident radiation 1000 and therefore corresponding pixel assignment. Asabove, electrical interconnect 1450 may be grounded or be at some otherreference potential. In some embodiments, electrical interconnect 1450may be electrically connected with the corresponding electrode of otherpixels (for example, through underlying layers of interconnect) so thevoltage may be applied across the pixel array. In other embodiments, theinterconnect 1450 may extend linearly across multiple pixel regions toform a common electrode across a row or column.

FIG. 3 e illustrates open interdigitated patterns where the patterns donot generally form a closed pattern and possess some form ofinterdigitation. The open interdigitated patterns may include a positiveinterconnection 1452 and ground (or other reference potential)interconnection 1450. This configuration may capture charge developedwithin the area between the two electrical interconnects and attract andmove the charge to the positively-biased electrical interconnect 1452.An array including separated open interdigitated structures may providea charge isolation system that may be used to identify a position ofincident radiation 1000 and therefore corresponding pixel assignment. Asabove, the interconnect 1450 may form a common electrode with adjacentpixel regions in some embodiments.

FIG. 3 f shows a two-row by three-column sub-region within a generallylarger array of top-surface electrodes. The array of electrical contactsprovides electrical communication to an overlying layer of opticallysensitive material. 1401 represents a common grid of electrodes used toprovide one shared contact to the optically sensitive layer. 1402represents the pixel-electrodes which provide the other contact forelectrical communication with the optically sensitive layer. Inembodiments, a voltage bias of −2 V may be applied to the common grid1401, and a voltage of +2.5 V may be applied at the beginning of eachintegration period to each pixel electrode 1402. Whereas the commoncontact 1401 is at a single electrical potential across the array at agiven time, the pixel electrodes 1402 may vary in time and space acrossthe array. For example if a circuit is configured such that the bias at1402 varies in relation to current flowing into or out of 1402, thendifferent electrodes 1402 may be at different biases throughout theprogress of the integration period. Region 1403 represents thenon-contacting region that lies between 1401 and 1402 within the lateralplane. 1403 is generally an insulating material in order to minimizedark current flowing between 1401 and 1402. 1401 and 1402 may generallyconsist of different materials. Each may for example be chosen forexample from the list: TiN; TiN/Al/TiN; Cu; TaN; Ni; Pt; and from thepreceding list there may reside superimposed on one or both contacts afurther layer or set of layers chosen from: Pt, alkanethiols, Pd, Ru,Au, ITO, or other conductive or partially conductive materials.

In example embodiments using the above structures, interconnect 1452 mayform an electrode in electrical communication with a capacitance,impurity region on the semiconductor substrate or other charge store. Insome embodiments, a voltage is applied to the charge store anddischarges due to the flow of current across the optically sensitivefilm over an integration period of time. At the end of the integrationperiod of time, the remaining voltage is sampled to generate a signalcorresponding to the intensity of light absorbed by the opticallysensitive layer during the integration period. In other embodiments, thepixel region may be biased to cause a voltage to accumulate in a chargestore over an integration period of time. At the end of the integrationperiod of time, the voltage may be sampled to generate a signalcorresponding to the intensity of light absorbed by the opticallysensitive layer during the integration period. In some exampleembodiments, the bias across the optically sensitive layer may vary overthe integration period of time due to the discharge or accumulation ofvoltage at the charge store. This, in turn, may cause the rate ofcurrent flow across the optically sensitive material to also vary overthe integration period of time. In addition, the optically sensitivematerial may be a nanocrystal material with photoconductive gain and therate of current flow may have a non-linear relationship with theintensity of light absorbed by the optically sensitive layer. As aresult, in some embodiments, circuitry may be used to convert thesignals from the pixel regions into digital pixel data that has a linearrelationship with the intensity of light absorbed by the pixel regionover the integration period of time. The non-linear properties of theoptically sensitive material can be used to provide a high dynamicrange, while circuitry can be used to linearize the signals after theyare read in order to provide digital pixel data. Example pixel circuitsfor read out of signals from pixel regions are described further below.

In some embodiments, the optically sensitive material in each pixelregion is a nanocrystal material and has symmetric properties when thepolarity of the bias is reversed. In some embodiments, the voltage oninterconnect 1450 (which may be a common electrode for the pixel array)may be varied during the read out cycle rather than held at ground or aconstant reference potential. For example, the voltage may be varied toreset or control the pixel circuit during transitions of the read outcycle as described further below.

The above photoconductor structures are examples only and otherstructures may be used on other embodiments.

Some of the properties and characteristics of example embodiments ofphotodetectors will now be described. These properties andcharacteristics may be tailored based on the nanocrystal materials thatare used, the bias that is applied and the size and geometry of thepixel regions. Example nanocrystal materials and methods of making thesame are described further below. Example embodiments may include any ofthese optically sensitive layers used in the photodetector structuresdescribed above or elsewhere in this specification and the resultingphotodetector structures may be used in example embodiments with any ofthe pixel circuits and system circuitry described below in thisspecification. These combinations are examples only and the nanocrystalmaterials and photodetector structures may be used in other embodimentsas well.

In some example embodiments, photodetectors of the type described abovemay have one or more of the following properties:

be readily integrable with other circuitry related to the image sensingfunction, such as circuits which store charge, circuits which relaysignal levels to the periphery of the array, circuits which manipulatethese signal levels in the analog domain, circuits which convert analoginto digital signals, and circuits which process image-related data inthe digital domain.

provide a maximum of sensitivity to light within the wavelength band, orbands, of interest. Sensitivity is often quantified using the measuresignal-to-noise (SNR) at a given level of illumination. Signal ismaximized when the responsivity, quantum efficiency, or gain of thedevice is maximized. Noise is minimized when random fluctuations inelectronic signals are minimized, subject to the limits prescribed bynatural fluctuations in electrical currents and voltages at a giventemperature. Relatedly, noise and other uncontrolled ordifficult-to-predict variations in background signal are generallyminimized when the magnitude of dark current is minimized. For this andother reasons, photodetectors having high sensitivity and low darkcurrent may be desired in many embodiments.

provide a response in time that is suitably fast. Applications such asvideo imaging and shutterless still-image acquisition typically requirephotodetectors whose signal levels change substantially completely inresponse to a transient within fewer than 100 milliseconds (10 framesper second), or fewer than 33 milliseconds (30 frames per second), oreven 1 millisecond ( 1/1000 second exposure of a still image).

provide for the detection of a wide range of light intensities in amanner that can conveniently be processed by available electroniccircuitry. This feature is known as providing high dynamic range. Onemeans of providing high dynamic range is to compress the measuredelectronic response as a function of the incident optical stimulus. Suchcompression may be referred to as a sublinear, i.e. a nonlinear withdecreasing slope, dependence of electrical signal on incident intensity.High dynamic range may also be facilitated by employing a photodetectorwhose gain may be controlled, such as through the selection of a voltagebias known to produce a specific gain.

provide for the convenient discrimination among different spectral bandsof electromagnetic radiation. Of particular interest are the x-ray,ultraviolet, visible (including blue, green, and red), near-infrared,and short-wavelength infrared bands.

Example embodiments may provide photoconductors and arrays ofphotodetectors, that possess one or more of these properties incombination as follows:

the photodetectors in example embodiments can readily be integrated withother portions of the image sensor circuit and system bystraightforward, low-cost methods such as spin-coating, spray-coating,drop-coating, and self-assembly. Embodiments include exchanging ligandspassivating nanoparticle surfaces for shorter ligands that will providefor appropriate charge carrier mobilities once films are formed.Embodiments include solution-phase exchanges which enable therealization of smooth-morphology films necessary to the realization ofimage sensors having acceptable consistent dark currents andphotoresponses across an array.

The photodetectors in example embodiments can provide a maximum ofsensitivity through a combination of means. They maximize signal byproviding photoconductive gain. Typical values for photoconductive gainrange from 1-10, resulting in responsivities in, for example, thevisible wavelengths ranging from 0.4 A/W to 4 A/W. In embodiments, thephotodetectors described herein minimize noise by fusing nanocrystalcores such as to ensure substantially non-noise-degrading electricalcommunication among the particles making up the optically sensitivelayer through which current flows. In embodiments, the photodetectorsdescribed herein minimize dark current by minimizing the net doping ofthe active layer, thus ensuring that the dark carrier density, and thusthe dark conductance, of these optically sensitive materials isminimized. In embodiments, the photodetectors described herein minimizedark current by providing an electrode-to-nanocrystalline-layerelectrical connection that blocks typically one type of carrier,including potentially the majority carrier at equilibrium. Inembodiments, cross-linking molecules are employed that utilize chemicalfunctionalities that remove oxides, sulfates, and/or hydroxidesresponsible for p-type doping. Thus, in embodiments, a more intrinsic oreven n-type optically sensitive layer may be provided, leading tolowered dark currents. In embodiments, many steps in quantum dotsynthesis and/or processing and/or device packaging may be performed ina controlled environment such as a Schlenk line or Glove Box; andoptically sensitive layers may be encapsulated using substantiallyimpermeable layers such as oxides, oxynitrides, or polymers such asparylene, or epoxies, in order to prevent reactive gases such as oxygenor water from significantly permeating the optically sensitive layer. Inthis manner, desired combinations of properties such as gain, darkcurrent, and lag may be preserved over the desired useful lifetime of animage sensor.

The photodetectors in example embodiments provide a time-domain responsethat can be as rapid as sub-100-milliseconds, sub-30-milliseconds, andsub-1-millisecond. In embodiments, this is achieved by providinggain-providing (and persistence-providing) trap states associated withthe optically sensitive layer that trap at least one type of carrier foronly a limited time period such as 100 milliseconds, 30 milliseconds, or1 millisecond. In some embodiments, PbS nanoparticles are decorated withPbSO3, an oxide of PbS, which is shown to have a trap state lifetime inthe vicinity of 20-30 milliseconds, providing for a transient responsesuited to many video imaging applications. In some embodiments,photodiodes are instead provided based on colloidal quantum dot layers,wherein two electrical contacts having appreciably different workfunctions are employed to contact the active layer. In some embodiments,dark currents may be minimized through operation of such devices withoutthe application of an appreciable external voltage bias. In someembodiments, cross-linking moieties such as benzenedithiol, a bidentatelinker, may be employed to remove and/or passivate certain trap statesthat may be present, or may develop, in such materials.

The photodetectors in example embodiments provide a means of enhancingdynamic range by producing a sublinear dependence of electrical signal(such as photocurrent). Over a region of low to middling intensities,trap states are available to become filled, and escape occurs followingsome moderate persistence, or trap state, lifetime, such as 30milliseconds for example. At higher intensities, these trap statesbecome substantially filled, such that charge carriers experienceshorter lifetimes, or persistence times, corresponding to lowerdifferential gains. As a result these devices exhibit substantiallyconstant gains over a range of low to middling intensities, followed bya gentle roll-off in gain at higher intensities. Put another way, at lowto middling intensities, photocurrent depends approximately linearly onintensity, but at higher intensities, photocurrent exhibits sublineardependence on intensity. In embodiments, photodetectors are providedwherein photoconductive gain depends on the bias applied to a device.This arises because gain is proportional to carrier lifetime divided bycarrier transit time, and transit time varies in inverse proportionalitywith applied field. In embodiments, circuits are developed that exploitthis dependence of gain on bias to increase dynamic range.

In example embodiments, photodetectors may readily be altered, or‘tuned’, to provide sensitivity to different spectral bands. One meansof tuning is provided through the quantum size effect, wherebynanoparticle diameter is decreased, in cases through synthetic control,to increase the effective bandgap of the resulting quantum dots. Anothermeans of tuning is provided through the choice of materials composition,wherein the use of a material having a larger bulk bandgap generallyfacilitates the realization of a photodetector with responsivity onsetat a higher photon energy. In embodiments, photodetectors havingdifferent absorption onsets may be superimposed to form vertical pixels,wherein pixel(s) closer to the source of optical signal absorb and sensehigher-energy bands of electromagnetic radiation, whereas pixel(s)further from the source of optical signal absorb and sense lower-energybands.

In a particular example embodiment of a photodetector 1400, asolution-processed route to ultrasensitive photodetectors 1400 (e.g.,D*˜10¹³ Jones) comprises synthesizing PbS colloidal quantum dots,exchanging their organic capping ligands in solution, forming thin filmphotodetectors by spin-coating, and implementing a developing step tomodify conductivity and modify trap states, resulting in photoconductivegains such as 1.5, 2, 5, 10, 20, 50, or 100 (See for example:Konstantatos, G. et al. Ultrasensitive solution-cast quantum dotphotodetectors. Nature 442, 180-183 (2006)). The photodetector 1400 mayemploy an infrared or a visible bandgap.

In another embodiment of a photodetector 1400, a thin-film photodetector1400 may be coated onto a chip. The thin-film photodetector 1400 may bemore sensitive than example silicon photodiodes and may provide built-ingain which may simplify read-out circuit design. The use of abias-dependent and/or intensity-dependent gain may enable enhanceddynamic range. The photodetector 1400 may employ colloidal quantum dots1200 which may offer an advantage over conventional bulk semiconductors,such as crystalline, amorphous, or organic, in that the quantum dots arequantum size-effect tunable. The thin-film photodetector 1400 maycomprise a stacked multi-spectral pixel which may incorporate use of thequantum size-effect tenability of the quantum dots 1200. The thin-filmphotodetector 1400 may be formed from quantum dot materials 200 subjectto a post-film-formation treatment wherein long, insulating ligands maybe exchanged for short ones, which may lead to highly sensitive visiblephotodetectors 1400. Thin-film post-processing may enable theintegration of top-surface thin-film photodetectors 1400 withcrystalline silicon. The photodetector 1400, across the entire visiblespectrum, may exhibit a normalized detectivity D*˜10¹³ Jones. Thephotodetector 1400 may exhibit photoconductive gains greater than unity,and ranging from 1.5 to 100, facilitating high-fidelity electronicread-out. The photodetector 1400 may enable between 3 dB and 20 dBgreater dynamic range than provided in a constant-gain photodetector.The photodetector 1400 exploits quantum size effect tunability todemonstrate a stacked multicolor pixel.

The thin-film photodetector 1400 of example embodiments may meetdemanding performance requirements including but not limited tosensitivity, gain, tunability, and dynamic range to name a few. Theperformance characteristics of some example embodiments are described inturn below.

Regarding sensitivity, a top-surface visible-wavelength photodetector1400 for visible imaging may ideally meet or exceed silicon'ssensitivity. One measure of sensitivity may be the noise-equivalentpower NEP, the minimum incident optical power that a device candistinguish from noise. However, since noise current in a photodetectormay not scale linearly with area, a quantity known as the normalizeddetectivity D*, with units of cmHz^(1/2) W⁻¹ (“Jones”), is defined. Thefigure of merit D* is equal to the square root of the optically activearea of the detector divided by its noise equivalent power (NEP). D*enables comparison between photodetectors of different areas.

Regarding gain, example silicon photodiodes may provide up to oneelectron's worth of current per incident photon. Under low-lightconditions, and especially in small pixels, this may necessitate the useof extremely low-noise electronic amplifying circuits. Ideally, aphotodetector would provide built-in gain, allowing for multiplecarriers to be collected in pixel circuitry per absorbed photon, thuslessening demands on read-out circuitry. For example, in photoconductivephotodetectors 1400, the creation of an electron-hole pair uponabsorption of a photon may result in an increase in conductivity thatpersists for the excited carrier lifetime.

As for tunability, quantum size-effect tuning may enable selecting thesemiconductor bandgap according to the needs of the application. Forvisible imaging, the optimal-bandgap sensor material would absorb onlyvisible light, obviating the need for an infrared cutoff filter and, bymaximizing bandgap, minimizing recombination-generation noise. A tunablematerials system also enables a stacked pixel architecture, wherein alarge-bandgap photodetector senses, and also filters out, higher-energylight, passing only the longer-wavelength light to theindependently-read pixel elements beneath. Such architectures offerimproved low-light sensitivity compared to (lossy) absorbent colorfilter arrays.

For dynamic range, the ratio of full-well capacity of CMOS image sensorsto the number of dark electrons limits dynamic range to about 3 ordersof magnitude in intensity (conventionally expressed as 60 dB inimaging). A photodetector 1400 may provide at least this much dynamicrange. A photodetector 1400 may, by virtue of its bias-tunable gainand/or its intensity-dependent gain, allow controlled signal compressionfor dynamic range enhancement.

Nanocrystal material exhibiting the above properties and methods ofmaking the same are described in further detail below.

Quantum Dot Pixel 1800

In the example embodiment of FIG. 1, the nanocrystal materials andphotodetector structures described above may be used to provide quantumdot pixels 1800 for a photosensor array, image sensor or otheroptoelectronic device. In example embodiments, the pixels 1800 includequantum dot structures 1100 capable of receiving radiation 1000,photodetectors structures adapted to receive energy from the quantum dotstructures 1100 and pixel structures. The quantum dot pixels describedherein can be used to provide the following in some embodiments: highfill factor, potential to bin, potential to stack, potential to go tosmall pixel sizes, high performance from larger pixel sizes, simplifycolor filter array, elimination of de-mosaicing, self-gainsetting/automatic gain control, high dynamic range, global shuttercapability, auto-exposure, local contrast, speed of readout, low noisereadout at pixel level, ability to use larger process geometries (lowercost), ability to use generic fabrication processes, use digitalfabrication processes to build analog circuits, adding other functionsbelow the pixel such as memory, A to D, true correlated double sampling,binning, etc. Example embodiments may provide some or all of thesefeatures. However, some embodiments may not use these features.

FIG. 7 c shows a schematic cross-section of an example imaging systemshown in FIG. 8. In an example embodiment, the QD Layer 1820 may includea continuous film of cross-linked nanocrystal cores, such as linked PbSnanocrystal cores, with trap states formed using oxidized core material,such as PbSO3. The QD Layer 1820 may provide photoconductive gain andhave a non-linear relationship between the rate of current flow throughQD Layer 1820 and the intensity of light absorbed by the QD Layer 1820.

In example embodiments, the imaging system of FIG. 7 c includes aread-out structure that includes a substrate 1812, an opticallysensitive layer 1820, e.g., QD layer 1820 and a transparent electrode1818. Substrate 1812 includes a read-out integrated circuit (ROIC)having a top surface with an array of pixel electrodes 1814 located inthe top surface thereof with counter-electrodes 1818 located outside thearray, i.e., transparent electrode 1818 overlaying QD layer 1820.Electrodes 1814 shown in FIG. 7 c correspond to square electrode pads300 shown in FIG. 8. The array of electrodes 1814, which together formfocal plane array 1810, provide voltages for biasing and currentcollection from a given pixel 1814 of the array, and convey signals fromthe array to an input/output electrode 1812 (connection not shown).Optically sensitive layer 1820, e.g., QD layer, is formed on the topsurface of the integrated circuit. More specifically, QD layer 1820overlays the array of pixel electrodes 1814 on the top surface of theintegrated circuit. The optically sensitive layer 1820 defines an arrayof imaging pixels for collecting radiation 1000 incident thereon.

In the imaging system of FIG. 7 c, QD layer 1820 is monolithicallyintegrated directly onto the electronic read-out chip.

Referring now to FIG. 7 d, there is shown at 1822 a side view of a basicoptical device structure, which in certain embodiments can be used as anindividual pixel in the completed integrated array shown in FIGS. 7 d-f.Device 1822 includes substrate 1824, which may be glass or othercompatible substrate; contact/electrode 1828; optically sensitive layer,e.g., QD layer 1832; and at least partially transparent contact 1830that overlays the QD layer. As above, QD layer 1832 may be a continuousfilm of cross-linked nanocrystal cores with trap states formed usingoxidized core material in example embodiments. Contacts 1828 and 1830may include, e.g., aluminum, gold, platinum, silver, magnesium, copper,indium tin oxide (ITO), tin oxide, tungsten oxide, and combinations andlayer structures thereof, and may include band-pass or band-blockfilters that selectively transmit or attenuate particular regions of thespectrum which are appropriate to the end use of the device. The devicehas an overall “vertical sandwich” architecture, where differentcomponents of the device generally overlay other components. Inoperation, the amount of current that flows and/or the voltage betweencontact 1830 and contact 1828 is related to a number of photons receivedby QD layer 1832. In operation, current generally flows in the verticaldirection. The embodiment shown in FIG. 7 d may also include one or moreadditional optional layers for electron/hole injection and/or blocking.The layer(s) allows at least one carrier to be transported, or blocked,from an electrode into the QD layer. Examples of suitable layers includea QD layer including QDs of a different size and/or composition,semiconducting polymers, and semiconductors such as ITO and Si.

Referring now to FIG. 7 e, there is shown at 1822 a a side view of abasic device structure that has a different configuration than eachpixel in the completed integrated array shown in FIGS. 7 d-7 f, butwhich could be used to form a similarly functioning optical device. Asabove, the QD layer 1832 a may be a continuous film of cross-linkednanocrystal cores with trap states formed using oxidized core materialin example embodiments. The configuration in FIG. 7 e corresponds to alateral planar structure in which the optically sensitive layer 1832 ais deposited across two spaced contacts/electrodes 1828 a and 1832.Contacts 1828 and 1832 are deposited on a substrate, e.g., glasssubstrate 1824 b. The integrated circuit, including contacts 1828 a,1832, and substrate 1824 b may include any appropriate system with whichthe optically sensitive material is compatible (e.g., Si, glass,plastic, etc.). Contacts 1828 b and 1832 may include aluminum, gold,platinum, silver, magnesium, copper, tungsten, tantalum, tungstennitride, tantalum nitride, indium tin oxide (ITO), tin oxide, tungstenoxide, or combinations or layer structures thereof. The device has anoverall “lateral planar” architecture, where at least some of thecomponents of the device are generally laterally displaced from othercomponents, forming a planar electrode structure. In operation, theamount of current that flows and/or the voltage between contact 1828 aand contact 1832 is related to a number of photons received by the QDlayer 1832 a. In operation, current generally flows in the lateraldirection.

FIG. 7 f shows a plan view of another basic device structure 1822 b thatincludes interdigitated electrodes, and which also can be used to forman optical device. The materials may be selected from those providedabove regarding FIGS. 7 d-7 e. As above, QD layer 1832 b may be acontinuous film of cross-linked nanocrystal cores with trap statesformed using oxidized core material in example embodiments.

Each basic device 1822, 1822 a, and 1822 b as shown in FIGS. 7 d-7 f,among other possible architectures, can be thought of as representing asingle device or an element in a larger device, such as in a lineararray or a two-dimensional array. The basic devices can be used in manykinds of devices, such as detection and signal processing, as discussedabove, as well as in emission and photovoltaic devices. Not allembodiments need be optical devices. Many QD layers have opticalcharacteristics that can be useful for optical devices such as one ormore of: image sensors useful in one or more radiation 1000 bands of theelectromagnetic spectrum; optical spectrometers including multispectraland hyperspectral; communications photodetecting optical receivers aswell as free-space optical interconnection photoreceivers; andenvironmental sensors. Some QD layers also have electricalcharacteristics that may be useful for other kinds of devices, such astransistors used in signal processing, computing, power conversion, andcommunications.

In one embodiment, the underlying electrodes on the integrated circuitdefine imaging pixels in an imaging device. The QD layers formed on theelectrodes supply optical-to-electrical conversion of incident radiation1000.

In another embodiment, in addition to the definition of pixels viaelectrodes on the integrated circuit, further patterning of theoptically sensitive layers, e.g., QD layers, provides further definitionof pixels, including of which pixel is read by which electrodes on theintegrated circuit. This patterning may also be accomplished withwell-known CMOS techniques such as photolithography. Other optionsinclude self-assembly of QD layers onto pre-patterned metal layers, suchas Au, to which the QDs and/or their ligands have a known affinity.Patterning may also be achieved by depositing a conformal QD layer ontoa topologically-variable surface, e.g., including “hills” (protrusions)and “valleys” (trenches) and subsequently planarizing the QD film toremove material accumulated on the “hills” while preserving that in the“valleys.”

Further layers may be included in the layers atop the structure, such aselectrical layers for making electrical contact (e.g. an at leastpartially transparent contact such as indium tin oxide, tin oxide,tungsten oxide, aluminum, gold, platinum, silver, magnesium, copper, orcombinations or layer structures thereof), antireflection coatings (e.g.a series of dielectric layers), or the formation of a microcavity (e.g.two mirrors, at least one formed using nonabsorbing dielectric layers),encapsulation (E.G. a substantially transparent dielectric such assilicon nitride (Si3N4) or silicon dioxide, or e.g. an epoxy or othermaterial to protect various materials from environmental oxygen orhumidity), or optical filtering (e.g. to allow one radiation 1000 bandto pass and a second radiation 1000 band not to)

The integrated circuit may include one or more semiconducting materials,such as, but not limited to silicon, silicon-on-insulator,silicon-germanium layers grown on a substrate, indium phosphide, indiumgallium arsenide, gallium arsenide, or semiconducting polymers such asMEH-PPV, P3OT, and P3HT. The integrated circuit may also include one ormore semiconducting organic molecules, non-limiting examples beingend-substituted thiophene oligomers (e.g. alpha,w-dihexyl hexathiophene(DH6T)) and pentacene. Polymers and organic molecules can be useful as asubstrate in the QD devices because they may be flexible, and thus allow“bendable” and “conformable” devices to be made that are thusnon-planar.

Other appropriate substrates may include, e.g., plastic and glass.

The above quantum dot pixels are examples only and other embodiments mayuse other pixel structures.

Pixel Circuitry 1700 (Including Other Components 1900)

Pixel circuitry that may be used to read out signals from thephotoconductive pixel regions will now be described. As described above,in embodiments, pixel structures 1500 within the QDPC 100 of FIG. 1 mayhave pixel layouts 1600, where pixel layouts 1600 may have a pluralityof layout configurations such as vertical, planar, diagonal, or thelike. Pixel structures 1500 may also have embedded pixel circuitry 1700.Pixel structures may also be associated with the electricalinterconnections 1404 between the photodetector structures 1400 andpixel circuitry 1700.

In embodiments, quantum dot pixels 1800 within the QDPC 100 of FIG. 1may have pixel circuitry 1700 that may be embedded or specific to anindividual quantum dot pixel 1800, a group of quantum dot pixels 1800,all quantum dot pixels 1800 in an array of pixels, or the like.Different quantum dot pixels 1800 within the array of quantum dot pixels1800 may have different pixel circuitry 1700, or may have no individualpixel circuitry 1700 at all. In embodiments, the pixel circuitry 1700may provide a plurality of circuitry, such as for biasing, voltagebiasing, current biasing, charge transfer, amplifier, reset, sample andhold, address logic, decoder logic, memory, TRAM cells, flash memorycells, gain, analog summing, analog-to-digital conversion, resistancebridges, or the like. In embodiments, the pixel circuitry 1700 may havea plurality of functions, such as for readout, sampling, correlateddouble sampling, sub-frame sampling, timing, integration, summing, gaincontrol, automatic gain control, off-set adjustment, calibration, offsetadjustment, memory storage, frame buffering, dark current subtraction,binning, or the like. In embodiments, the pixel circuitry 1700 may haveelectrical connections to other circuitry within the QDPC 100, such aswherein other circuitry located in at least one of a second quantum dotpixel 1800, column circuitry, row circuitry, circuitry within thefunctional components 2004 of the QDPC 100, or other features 2204within the integrated system 2200 of the QDPC 100, or the like. Thedesign flexibility associated with pixel circuitry 1700 may provide fora wide range of product improvements and technological innovations.

Pixel circuitry 1700 within the quantum dot pixel 1800 may take aplurality of forms, ranging from no circuitry at all, justinterconnecting electrodes, to circuitry that provides functions such asbiasing, resetting, buffering, sampling, conversion, addressing, memory,and the like. In embodiments, electronics to condition or process theelectrical signal may be located and configured in a plurality of ways.For instance, amplification of the signal may be performed at eachpixel, group of pixels, at the end of each column or row, after thesignal has been transferred off the array, just prior to when the signalis to be transferred off the chip 2000, or the like. In anotherinstance, analog-to-digital conversion may be provided at each pixel,group of pixels, at the end of each column or row, within the chip's2000 functional components 2004, after the signal has been transferredoff the chip 2000, or the like. In addition, processing at any level maybe performed in steps, where a portion of the processing is performed inone location and a second portion of the processing is performed inanother location. An example may be the performing analog-to-digitalconversion in two steps, say with an analog combining at the pixel 1800and a higher-rate analog-to-digital conversion as a part of the chip's2000 functional components 2004.

In embodiments, different electronic configurations may requiredifferent levels of post-processing, such as to compensate for the factthat every pixel has its own calibration level associated with eachpixel's readout circuit. The QDPC 100 may be able to provide the readoutcircuitry at each pixel with calibration, gain-control, memoryfunctions, and the like. Because of the QDPC's 100 highly integratedstructure, circuitry at the quantum dot pixel 1800 and chip 2000 levelmay be available, which may enable the QDPC 100 to be an entire imagesensor system on a chip. In some embodiments, the QDPC 100 may also becomprised of a quantum dot material 200 in combination with conventionalsemiconductor technologies, such as CCD and CMOS.

Pixel circuitry may be defined to include components beginning at theelectrodes in contact with the quantum dot material 200 and ending whensignals or information is transferred from the pixel to other processingfacilities, such as the functional components 2004 of the underlyingchip 200 or another quantum dot pixel 1800. Beginning at the electrodeson the quantum dot material 200, the signal is translated or read. Inembodiments, the photoconductive photovoltaic quantum dot material 200may act as a resistor that changes its resistance in response toradiation 1000. As such, the quantum dot pixel 1800 may require biascircuitry 1700 in order to translate the resistance to a readablesignal. This signal in turn may then be amplified and selected forreadout. One embodiment of a pixel circuit shown in FIG. 6 a uses areset-bias transistor 1802, amplifier transistor 1804, and columnaddress transistor 1808. This three-transistor circuit configuration mayalso be referred to as a 3T circuit. Here, the reset-bias transistor1802 connects the bias voltage 1702 to the photoconductive photovoltaicquantum dot material 200 when reset 1704 is asserted, thus resetting theelectrical state of the quantum dot material 200. After reset 1704, thequantum dot material 200 may be exposed to radiation 1000, resulting ina change in the electrical state of the quantum dot material 200, inthis instance a change in voltage leading into the gate of the amplifier1804. This voltage is then boosted by the amplifier transistor 1804 andpresented to the address selection transistor 1808, which then appearsat the column output of the address selection transistor 1808 whenselected. In some embodiments, additional circuitry may be added to thepixel circuit to help subtract out dark signal contributions. In otherembodiments, adjustments for dark signal can be made after the signal isread out of the pixel circuit.

In embodiments, the impedance of the quantum dot material 200 may bevery high, such as in the one teraohm range, making integration timesfor a dark scene in the milliseconds range, while the integration timesfor a bright scene may be in the microseconds range. Additionally, theresponse curve may not be linear, resulting in an S-shaped responsecurve. This type of response curve may require modification of how the3T circuit is used, relative to what is conventional for a photodiodeconfiguration. For instance, a conventional 3T reset is digital, withthe reset off during integration and the totally on during reset. Thereset of the QDPC 100 3T circuit, is analog, varying in voltage, forexample in some embodiments from 0V to 1.8V continuously, biasing to geta particular shape and optimization of response. Reset for the QDPC 100circuit may also be turned on harder during reset, and weaker duringintegration, but may always be supplying a bias voltage, which mayprovide greater control of the circuit. Also, as mentioned previously, aphotodiode may have a very large capacitance, say 50-100 femtofarads,with a gain of less than unity. The QDPCs 100 quantum dot material 200has a very low capacitance, say less than one femtofarad, with a largerange of gain, say between 0.1 and 10,000, depending on the bias.

Control timing of the conventional 3T circuit is characterized by fixedvoltages and timing, such as the reset voltage turning on hard and thenback down to zero at the end of a frame interval, and the timing betweenframes being fixed. In the QDPC 100 3T circuit, reset voltages may vary.Also, the timing is variable for the QDPC because the quantum dotmaterial 200 response curve is not linear as it is for a photodiode,where the slope is directly dependent on the amount of radiation 1000and saturation can be reached. In the quantum dot material 200 response,the relationship is exponential, where strong radiation 1000 may producea sharp decay and a weak radiation 1000 may produce a very slow decay.Because of this response, there is not voltage level where saturation isreached, and thus there is no limit on the dynamic range. For instance,over a range of one nanowatt to one milliwatt of radiation 1000intensity, the QDPC 100 may experience a 360 millivolt output range,which is easy to read.

Although additional circuitry may not be required for the low noiseoperation of the QDPC 100 in some embodiments, a fourth transistorcircuit group may be added to increase sensitivity. FIG. 6 b shows aQDPC 100 4T circuit, with the fourth transistor 1708 configured as asample and hold. This configuration may also be referred to as a globalshutter, where the entire pixel 1800 array may be sampled at the sametime, but not necessarily at a fixed time, where the time of samplingmay be a function of radiation 1000 conditions. The sample and hold mayimplement a correlated double sampling, where the signal value of eachpixel is transferred to the output, and the output is reset to areference value. The final value assigned to this pixel may be thedifference between the reference value and the transferred signal.Correlated double sampling may yield the best representation of the truevalue associated with each pixel. From an electronics standpoint, theremay be different methods for accomplishing this, such as digital, analogsample and hold, integration, dual slope, and the like. Differences ineffectiveness may become evident with ultra low noise systems of lessthan 4 or 5 electrons, depending on the overall design of the system. Inan embodiment, two sample and holds may be used, holding two values inorder to utilize the difference between them. In addition, the QDPC 4Tcircuit may also have a separate pixel reset, which may be distinct fromthe circuit reset. The two resets may be used simultaneously, or atdifferent times. In embodiments, the QDPC 100 circuits may have variedvoltages, time profiles, lengths of reset times, sampling schemes, andthe like, that my enable innovative product solutions not capable withconventional designs.

In embodiments, the biasing of the photodetector may be time invariantor time varying. Varying space and time may reduce cross-talk, andenable a shrinking the quantum dot pixel 1800 to a smaller dimension,and require connections between quantum dot pixels 1800. Biasing couldbe implemented by grounding at the corner of a pixel 1800 and dots inthe middle. Biasing may occur only when performing a read, enablingeither no field on adjacent pixels 1800, forcing the same bias onadjacent pixels 1800, reading odd columns first then the even columns,and the like. Electrodes and/or biasing may also be shared betweenpixels 1800. Biasing may be implemented as a voltage source or as acurrent source. Voltage may be applied across a number of pixels, butthen sensed individually, or applied as a single large bias across astring of pixels 1800 on a diagonal. The current source may drive acurrent down a row, then read it off across the column. This mayincrease the level of current involved, which may decrease read noiselevels.

In embodiments, current flow may be vectored, flowing down through aseries of layers, for example. Applying a voltage or a current,collecting across a different set, referencing differentialmeasurements, that is the differences between pairs of electrodes, andresulting in DC offsets that are proportional to the offset signal.

In embodiments, configuration of the field, by using a biasing scheme orconfiguration of voltage bias, may produce isolation between pixels. Forexample, even if there were photoconductive photovoltaic material above,current may flow in each pixel so that only electron-hole pairs flowwithin that pixel. This may allow electrostatically implementedinter-pixel isolation and cross-talk reduction, without physicalseparation. This could break the linkage between physical isolation andcross-talk reduction. This type of scheme may be implemented with acheckerboard, non-contiguous grouping. In a Cartesian system bias couldbe create orientations that are opposite one another, so carriers maysee a potential minimum at the collection region, and scatter to thecenter of the pixels.

In embodiments, the pixel circuitry 1700 may include circuitry for pixelreadout. Pixel readout may involve circuitry that reads the signal fromthe quantum dot material 200 and transfers the signal to othercomponents 1900, chip functional components 2004, to the other features2204 of the integrated system 2200, or to other off-chip components.Pixel readout circuitry may include quantum dot material 200 interfacecircuitry, such as the 3T and 4T circuits shown in FIGS. 6 a and 6 b forexample. Pixel readout may involve different ways to readout the pixelsignal, ways to transform the pixel signal, voltages applied, and thelike. Pixel readout may require a number of metal contacts with thequantum dot material 200, such as 2, 3, 4, 20, or the like. Theseelectrical contacts may be custom configured for size, degree ofbarrier, capacitance, and the like, and may involve other electricalcomponents such a Schottky contact. Pixel readout time may be related tohow long the radiation 1000-induced electron-hole pair lasts, such asfor milliseconds or microseconds. In embodiments, this time my beassociated with quantum dot material 200 process steps, such as changingthe persistence, gain, dynamic range, noise efficiency, and the like.

Readout of the quantum dot pixel 1800 may be performed with a pluralityof signal transformation techniques, such as resistance-to-voltage,resistance-to-current, resistance-to-charge, feedback mode, combiningdark-current, or the like. Resistance-to-voltage may utilize a resisterdivider, where the quantum dot material 200 represents one resister andthe other is a dark resistor. In this scheme, a bias voltage is placeacross the pair, and the output voltage at the node between them ismonitored. In embodiments, the output response may be non-linear, andmay be a function of pixel 1800 size. Bias voltages may be a pluralityof values, including 1.8V, 2.5V, 3.3V, and the like, where it may bedesirable to use the largest voltage available in some embodiments. Insome embodiments, these voltages may be filtered, regulated,conditioned, or the like.

In embodiments, pixel readout may be performed with aresistance-to-current scheme, such as a constant current approach. Inlow radiation 1000, with constant current, resistance may start low,then increases higher on the slop transfer function. In embodiments, aconstant current scheme may require transistor circuits in theimplementation, translating into a greater amount of circuitry requiredthan other schemes, such as with constant voltage where only resistorsare involved. With transistor configurations there may also be issues oftransistor matching and offsets. A reference may also be required, suchas a self-reference, mirror circuit, self-reference switching, or thelike. Switching may improve charge rejection and switching noiseeffects. In embodiments, the constant current approach may represent animproved method for interfacing with a non-linear device, such as thequantum dot material 200, where radiation 1000 in low radiation 1000 mayrepresent a low slope, midrange the greatest slope, and bright radiation1000 back to a low slope again, a so called S-curve.

In embodiments, pixel circuitry may accommodate different ways toacquire the image, such as integration, sampling, or the like.Integration may involve exposures on the order of milliseconds, andpossibly involve the entire pixel 1800 array over an entire frameperiod. With large ranges of radiation 1000 intensity only generatingsmall voltages, such as 480 mV, there may be no need for gain, althoughautomatic gain control may still be implemented. In embodiments,exposure values may provide different mapping between optical intensityand sample voltage. The RC constant associated with dark resistance maydetermine longest exposure times. In embodiments, more conventionalarchitectures may be utilized in combination with new techniques toachieve longer exposure times.

In an alternate embodiment, the image may be sampled multiple timesduring a frame period, which may take advantage of the constantintegration that occurs in the quantum dot structures 1100. Sampling maybe for time periods on the order of microseconds, sampling one pixel,column, or cluster in secession during the frame period, which may be onthe order of a millisecond. This may result in a large number of samplestaken during the frame period, such as a thousand samples per frameperiod. In embodiments, the noise bandwidth may be larger, but withincreased noise due to the increased number of reads. However,simplicity may be gained, and may be traded against the additional noisedepending upon the application. In embodiments, all that may be neededis a single switch on each pixel 1800. Biasing may be applied the wholetime, but with only a brief sample, or biasing may be a limited periodof time. Sampling may utilize techniques similar to correlated doublesampling, reducing the total noise by subtracting off signal andbackground. This may help avoid low 1/f noise. In embodiments, variousintegration and sampling schemes may be applied to the operation of theQDPC 100, which may result in operational flexibility in the developmentof new product applications.

In embodiments, there may be calibration circuitry associated with thepixel circuitry 1700, such as performing or not performing dark currentsubtraction. Dark current subtraction may be performed with the use ofresistance bridges, or in circuitry at the end of rows or columns, or ateach individual pixel. Associated dark resistors may be covered andlocated at the end of rows, at the end of columns, at individual pixels,at the center of pixel groupings, within an area bounded be a group ofpixels, or the like. Calibration may then be performed by characterizingthe dark verses the regular pixel(s) in the appropriate ratios, and withrespect to resistance and geometry. The ratio of the covered darkresistor to the not covered pixel(s) may be referred to as fill factor,and may be minimized in order to maximize the exposed radiation 1000sensitive quantum dot material 200. Fill factors may be minimized bytiling groups of pixels, and may be configured in a plurality oforientations, such as orthogonal or non-orthogonal. Shielding of thedark resistor may be implemented by covering the dark resistor with ametal or other material. In an alternate embodiment, photodetectingsurfaces may be fabricated that are not sensitive to radiation 1000, orare desensitized or otherwise conditioned during fabrication, such as bymasked UV radiation. In embodiments, areas may be made radiation 1000sensitive though exposure to masked radiation, such as UV radiation. Inembodiments, dark references may be determined as the signals are readout of the array.

In embodiments, no dark current subtraction may be required. This may beenabled if the change in resistance of one photon is greater than thedark current, then the dark current may be ignored. This may speed upreadout, groups may perform their own self-calibration by measuring theresistance of each neighbor, because small groups may have similarillumination or be smaller than the resolution of the optics in thesystem. Differences may be due to dark current, gain offsets betweenpixels, transfer function for the optics, or the like. Resistancebridges may still be used, but now they may be used within theself-calibration group. This type of system may allow for dynamic,continuous adjustment, that may be user defined or set at the productionor user level. In embodiments, the use of techniques that enablecalibration without the need for dark resistors may create smaller,faster product applications.

In embodiments, calibration may involve the adjustment of pixel outputswith respect to preset calibration levels, gain calculations, comparisonwith neighboring pixels 1800, controlled sensitivity, power levels, orthe like. For instance, there may be areas of higher sensitivity andlower sensitivity within the quantum dot structure 1100 and it may bedesirable to calibrate, heighten the sensitivity, or reduce thesensitivity in certain areas to create a more flat response from thephotodetector. In embodiments, processing 2008 may have the ability tomonitor hot spots, exposure, sensitivity, or the like, across the pixel1800 array, and make adjustments through pixel circuitry 1700. Pixels1800 may be self-tuning, where they are able to optimize themselves tosome criteria. This criteria may be preset, or adjusted continuouslythrough on-chip processing 2008. Pixels 1800 may be able to adjust powerlevels, where dissipated power may be inversely proportional to theresponse, but dissipation normalizes the response. Pixels may be able toadjust their gain, timing, reset, or the like. In embodiments, theability of a pixel 1800 to be adjusted, or perform self-adjustment, maybe enabled through the presence of pixel electronics 1700.

Finally, the signal may be sent through decoding circuitry resident inthe pixel circuitry. This circuitry may be simpler because radiationdoes not have to pass through the substrate of the QDPC 100, andcircuits may perform better in darkness. The circuitry may be easier toaccommodate because of the availability of a larger number of layers andincreased circuit resources due to the increase integration density ofthe QDPC 100. In embodiments, decoding circuitry may be resident in thepixel circuitry, in the functional components 2004 within the underlyingchip 2000, or in the integrated system 2200, at the edges of the array,or scattered in various locations within the array. In embodiments,flexibility of where to place the decoder circuitry, or other components1900 such as memory, may allow for more flexible custom productapplications.

In embodiments, pixel binning may be employed, wherein the signalcorresponding to a multiplicity of smallest-patterned-pixels may beaccumulated within a single superpixel. The accumulation can be achievedin digital domain, in analog domain, or at film level. Take the exampleof accumulating the signal corresponding to a 2×2 array into a singlesuperpixel: It can be achieved using film binning by applying a biasacross the entire set of 2×2 pixels and integrating into a singlecapacitor. It can also be achieved using analog binning by sum up thecharge stored in the 4 individual capacitors, or using digital binningafter the signal is digitized.

In embodiments, the photocurrent passing through the photoconductivelayer, and collected in a given pixel, may have a nonlinear relationshipwith the intensity impinging on that pixel. In embodiments, thisnonlinear relationship may be sublinear, thus the photoconductive gainmay diminish with increasing intensity. In embodiments, it may bedesired to provide an estimate of the intensity impinging on the pixelduring the integration period based on the collected current. Inembodiments, it may be desirable to estimate the functional relationshipbetween intensity and photocurrent, Photocurrent=f(Intensity), and todetermine, or estimate, the inverse of this function,Intensity=f⁻¹(Photocurrent). In embodiments, the functional relationshipbetween intensity and photocurrent may be characterized duringproduction or assembly and a representation be stored on or off devicefor use by a post processing digital algorithm that will invert (f⁻¹)the intensity-photocurrent mapping function(f). In embodiments, a signalproportional to the inferred intensity may be generated, by theimplementation of an analog function that approximately inverts (f⁻¹)the intensity-photocurrent mapping function (f).

In embodiments, the voltage spacing among the levels of ananalog-to-digital converter may be manipulated, including being madenonuniform, such as to compensate for the nonlinear photocurrent vs.intensity relationship mentioned above. In some embodiments,analog-to-digital converters may be provided on the semiconductorsubstrate under the array of pixel region and in electricalcommunication with the respective pixel circuits. In some embodiments,analog-to-digital converters may be provided on the semiconductorsubstrate in a region adjacent to the photosensor array. In someembodiments, the analog-to-digital converters may compensate at leastpartially for the nonlinear photocurrent vs. intensity relationshipmentioned above. In other embodiments, the analog-to-digital convertersdo not include compensation for nonlinearity. In some embodiments,compensation for nonlinearity may be provided in digital circuitry afteranalog-to-digital conversion or by software on a digital processor onthe same chip (for example, a system-on-chip) or an another chip in thedigital camera or other system in which the image sensor is used.

In embodiments, further arithmetic operations may be implemented in thedigital domain to produce a revised digital estimate of the impingingintensity based on the observed digital estimate of the photocurrent oraccumulated photocharge.

Additional example embodiments of pixel circuits will now be described.FIGS. 12-19 illustrate aspects of additional pixel circuits that may beused in embodiments in combination with the example photoconductors andpixel regions described herein.

FIG. 12 is a circuit diagram of a 3T pixel circuit according to anembodiment. FIG. 12 is further explained with reference to the legendbelow.

Bias Voltages:

vbiasTX=nominal 2.8V-fixed

sf_drain=nominal 2.8V-fixed

vbiasR=adjustable: −2V to 2.8V

Signal Voltages:

vsrc=1.5V→2.5V

Vcol=1.5V→0.5V

Timing Control Signals:

sel=row select; 0→2.8V

rst=reset; 0→4V

Mrt=reset transistor

Msf=read-out buffer

Mrs=row-select transistor

The above biases, signal voltages and timing control signals areexamples only and other embodiments may use other values. In thisexample embodiment, the Film 4 may be a photoconductor with an opticallysensitive nanocrystal material as described above. In exampleembodiments, the current across Film 4 has a non-linear relationshipwith light intensity absorbed by the Film 4. Vsrc 11 is applied to theFilm 4 at one electrode and vbiasR is applied to the Film 4 at the otherelectrode, which results in a voltage difference across the Film 4. Inexample embodiments, the Film 4 provides photoconductive gain when thisbias is applied across the Film 4 as described above. The electrodes maybe in any of the photoconductor configurations described above or inother configurations. In some embodiments, this circuit may be used toread out one layer of a multi-layer or multi-region color pixel asdescribed further below.

When the example pixel circuit shown in FIG. 12 is operating, in orderto capture the photo current generated on Film (4), Iph, the resettransistor 1 is turned on by setting node 5 high enough (up to 4V,through an on-chip charge-pump/regulator circuit) so that node 11 willbe charge to a voltage equal to vbiasTX (node 6) which is typically setto the supply rail: 2.8V. This is the reset phase. Once this ‘reset’operation is completed, Node 5 is being set to 0V to turn off the resettransistor Mrt (1). In doing so, charge injection and parasiticcapacitive feedthrough effects will cause node 11, now becoming afloating node, to drop by approximately 300 mV. Therefore after the‘reset’ operation the actual ‘reset’ voltage value at node 11 isapproximately 2.5V.

At this time, the photo current s is being generated within Film (4),and the amount of photo current (photo sensitivity) generated isdependent on the voltage across the Film (4), i.e. (vsrc-vbiasR). WithvbiasR being able to be set arbitrarily to any voltage level from −2V to2.8V, the light sensitivity of the pixel can be adjusted.

The photo current from Film (4) discharges the parasitic capacitance atthe vsrc node (11) and its voltage level drops at a rate dependent onthe value of the parasitic capacitance at vsrc (node 11) as well as theequivalent conductance of the Film during the integration time.

After a specific integration time, the resulting integrated voltage atnode 11 will be read out through transistors Msf (2) and Mrs (3), thesource-follower buffer transistor and the Row-select transistor bysetting the node Sel (8) to a high level (2.8V).

In this example embodiment, the charge store that is discharged at node11 comprises parasitic capacitance of one or more of the transistorsthat are in electrical communication with the electrode of the pixelregion at vsrc (node 11). The electrode at vsrc (node 11) can be inelectrical communication with the gate of a transistor, such as Msf 2,which provides a parasitic capacitance. In one example embodiment, thecharge store may be provided at least in part by a parasitic capacitancebetween the gate and drain of the source follower transistor, Msf 2, anda parasitic capacitance between the source and substrate of the resettransistor, Mrt 1. These are parasitic capacitances between thestructures on the semiconductor substrate (poly, n-well and substrate)on which or in which the pixel circuit is formed. In an exampleembodiment, these parasitic capacitances may be in the range of about1-2 Femto Farads or more generally in the range of about 0.5 to 3 FemtoFarads or any range subsumed therein. The pixel region, opticallysensitive nanocrystal layer and electrodes may be formed in differentlayers above the regions of the semiconductor substrate used to form thetransistors Mrt 1, Msf 2 and Mrs 3. In an alternate embodiment, thepolarity of the bias could be reversed and the parasitic capacitance atvsrc could be charged instead of discharged during the integrationperiod.

FIG. 13 is a layout diagram showing a 4×4 pixel layout withillustrations of the location of the 3 transistors within the pixelread-out circuit described above. In the illustration, the geometrieslabeled as poly-gate1 and diffusion1 combine to form the resettransistor Mrt. The geometries labeled as poly-gate2 and diffusion2combine to form the source-follower buffer transistor Msf. Thegeometries labeled as poly-gate3 and diffusion2 combine to form therow-select transistor Mrs. The grid forming four squares over FIG. 13 isa common electrode that provides vbiasR for all four electrodes. In thecenter of each square is the pixel electrode at vsrc for each pixelregion. An optically sensitive nanocrystal material is coated over andin contact with these electrodes to form the four pixel regions. Thesepixel regions are formed in layers above the semiconductor substrate inwhich or on which the pixel circuit transistors (Mrt, Msf and Mrs) areformed. Vias and interconnect layers of the integrated circuit devicemay be used to provide the electrical connection between the pixelcircuit and the electrodes of the pixel regions.

FIGS. 14( a) and 14(b) depict the current-voltage dependencies of theoptoelectronic devices that are read in image sensor(s) based onconventional photodiodes vs (b) image sensors disclosed herein based onphotoconductive optically sensitive layers. The optically sensitivelayers (b) may be, in example embodiments, nanocrystal materials havingphotoconductive gain, such as PbS cores fused or linked in a continuousfilm with PbSO3 forming trap states on the outer surfaces of the coresto provide persistence as described herein).

Especially under no illumination, the asymmetry in the current vs.voltage dependence of the conventional photodiode of (a) is clear. Whenpositive bias is applied to the p-type side (deeper work function) sideof a p-n junction device, the current grows much more rapidly than if abias of the same amplitude, but of the opposite polarity, were applied.This feature is known as rectification.

In contrast, the symmetric current-voltage characteristic of aphotoconductor made using two contacts having similar work functions asone another is illustrated in (b). This device is nonrectifying: theamplitude of the flowing current is essentially invariant with thepolarity of bias.

Photodiodes are usually operated in reverse-bias mode. Underillumination, they typically provide a current of less than or equal tounit of current (electron) per photon incident (Quantum Efficiency is<=100%). Photoconductive photodetectors can, in contrast, exhibit gain,wherein the additional current that flows upon illumination can exceedone unit of current (electron) per photon incident. This is representedconceptually in the diagram (b) by the greater spacing between the 0lux, 1 lux, and 2 lux light levels in (b) (especially at higher bias)compared to (a).

It should also be noted that the responsivity of the photodiode issubstantially the same irrespective of the amplitude of the reverse-biasapplied to it; and, in general, does not exceed unity, even at highbias. In contrast, the responsivity, and the gain, of thephotoconductive photodetector increases approximately linearly with biasin the illustration of (b). This fact is exploited in certain circuitsdescribed herein in order to increase the dynamic range of thelight-sensing system.

FIGS. 15( a) and 15(b) show the voltage at vsrc (node 11 of FIG. 12) asa function of time for two cases: (a) A photodiode or (b) Aphotoconductive with bias-dependent gain. In (a), because the quantumefficiency is irrespective of bias, even as the capacitor discharges andthe voltage at vsrc decreases, decreasing the bias across thephotodiode, the rate of discharge remains fixed for a given illuminationlevel. In contrast, in (b), because the gain depends on bias, as thecapacitor discharges and the voltage at vsrc decreases, decreasing thebias across the photoconductor, the rate of discharge decreases for agiven illumination level.

As a consequence, in (a), in the example, only light levels 0-10 lux canbe contained within the (typical) 1 V output swing of the read-outcircuit which feeds into an analog-to-digital converter having 1 V inputswing. In contrast, in the example, light levels 0-100 lux are containedwithin the 1 V output swing of the read-out circuit which feeds into ananalog-to-digital converter having 1 V input swing.

FIG. 16 is a layout diagram for a 3T 1.4 um rectangular pixel accordingto an embodiment. This pixel has the same schematic diagram and circuitoperational description as the 3T 2.4 um pixel of FIG. 12. In order toachieve a much smaller pixel pitch, the underlying pixel read-outcircuit is laid-out in a rectangular fashion. Layout-mirroring is alsoused to further reduce the layout area. The following layout diagram ofa 4×4 pixel array illustrates this. Note that the photo-sensor pixel isa 4×4 array while the underlying pixel-read out circuit is arranged inan 8×2 fashion. The mirroring line is also shown in the layout, wherethe mirroring happens by mirroring the layout of the 8 pixels above thisline about the ‘mirroring line’ to form the bottom 8 pixel layout.

In FIG. 16 the geometries labeled as poly-gate1 and diffusion combine toform the reset transistor Mrt. The geometries labeled as poly-gate2 anddiffusion combine to form the source-follower buffer transistor Msf. Thegeometries labeled as poly-gate3 and diffusion combine to form therow-select transistor Mrs.

Although this pixel is typically considered to be a non-sharing pixel,in which there is no transistor sharing between pixels, the mirroringresults in a ‘shared-diffusion’ where the diffusion representing nodevcol (9) is shared between pixels above and below the mirroring line.This is where the area savings come about through mirroring. All thevcol nodes from all the pixels along the same column are electricallyconnected.

FIG. 20 c shows a layout for two pixel circuits. The top square in FIG.20 c is one pixel region and the bottom square is the other pixelregion. The pixel circuit is formed on the semiconductor substrate underthe pixel regions. The side-by-side rectangular regions on the right andleft of FIG. 20 c outline the layout of the pixel circuit for each pixelregion. In this embodiment, the pixel circuit for each pixel regionextends under one half of each pixel region. This layout, in which thepixel circuits are not confined to the space below the correspondingpixel region, allows for more flexibility in layout and may provide fora more compact pixel circuit layout.

FIG. 17 is a circuit diagram of a pixel according to another embodiment.The diagram is further explained with reference to the legend below.

Bias Voltages:

vbiasTX=nominal 2.8V-fixed

sf_drain=nominal 2.8V-fixed

vbiasR=adjustable: −2V to 2.8V

Signal Voltages:

vshare=1.5V→2.5V

Vcol=1.5V→0.5V

Timing Control Signals:

sel=row select; 0→2.8V

rst=reset; 0→4V

tx[0:4]=transfer switches; 0→4V

Mrt=reset transistor

Msf=read-out buffer

Mrs=row-select transistor

The operation of the circuit of FIG. 17 is similar in principal to thatof the 3T 2.4 um pixel of FIG. 12. In this particular design, thetransistors Mrt, Msf, Mrs are shared between 4 pixels. The TX[0:4]transistors are switches that isolate the 4 different pixels from theshared ‘floating diffusion’ or ‘− vshare (110).

The group of 4 pixels shown consists of 2 G(reen) pixels and 1 R(ed) andB(lue) pixels each, compatible to a Bayer pattern.

During the reset phase of each of the 4 pixels, for example the ‘R’pixel', node rst (5) and Tx[1] is set to a high voltage (in oneembodiment up to 4V, through an on-chip charge-pump/regulator circuit)so that node 110 and 101 will be charged to a voltage equal to vbiasTX(node 6) which is typically set to the supply rail: 2.8V. Once this‘reset’ operation is completed, Node 5 and Tx[1] are being set to 0V.Due to parasitic capacitance effects, the ‘reset’ voltage at node 101will be settled to ˜2.5V.

At this time, the photo current s is being generated within the pixel R,and the amount of photo current (photo sensitivity) generated isdependent on the voltage across the pixel, (e.g., 101-vbiasR). WithvbiasR being able to be set arbitrarily to any voltage level from −2V to2.8V, the light sensitivity of the pixel can be adjusted.

The photo current discharges the parasitic capacitance at 101 and itsvoltage level drops at a rate dependent on the value of the parasiticcapacitance at node 101 as well as the equivalent conductance of theFilm during the integration time.

After a specific integration time, the integrated voltage at node 101will be read out by ‘charge-sharing’ between node 110 and 110 throughturning on Tx[1]. In order to achieve that during a read-out, node rst(5) is first set to a high value (up to 4V) to set the node 110 to the‘reset’ voltage value (2.5V). Tx[1] will then be set to a high voltage(up to 4V), connected the nodes 101 and 110 to enabling the‘charge-sharing’ operation, through which integrated voltage at 101 willrise whereas the voltage at node 110 will drop until they equalize. Thisresulting voltage level is then read out through transistors Msf (2) andMrs (3), the source-follower buffer transistor and the Row-selecttransistor by setting the node Sel (8) to a high level (2.8V).

The read-out operation is the same for the other 3 pixels in the groupof 4 pixels.

FIG. 18 is a layout illustrating a 4×4 pixel array according to anembodiment. One group of 4-to-1 shared pixel as described above isreferenced in FIG. 16.

In some embodiments, pixel can change shapes from one layer to anotherlayer, while maintaining the same pixel area. For example, in quantumfilm layer the pixel region can have square shape while in silicon layerfor the pixel circuit has rectangular shape. As another example, if thefilm layer pixel is 2 um×2 um, the silicon layer pixel can be 4 um×1 um:so putting together 4 silicon layer pixels in a row gives a total areaof 4 um×4 um, which corresponds to 2×2 array of film layer pixels.Utilizing this pixel shape flexibility one can achieve very high pixelsharing such as 16-to-2 sharing, which means 16 pixels can be read outusing 2 sets of readout transistors. FIG. 20 b shows the layout for a16-2 shared pixel circuit in which transistors are shared among two setsof eight pixels.

FIG. 19 is a circuit diagram of a pixel according to another embodiment.The diagram is further explained with reference to the legend below.

Bias Voltages:

vbiasTX=nominal 0V-fixed

sf_drain=nominal 0V-fixed

vbiasR=adjustable: 0 to 4V

Signal Voltages:

vsrc=0.3V→1.3V

Vcol=1.3V→2.3V

Timing Control Signals:

sel=row select; 0→2.8V

rst=reset; 0→4V

Mrt=reset transistor

Msf=read-out buffer

Mrs=row-select transistor

To capture the photo current generated on Film (4), Iph, the resettransistor 1 is turned on by setting node 5 low (0V) so that node 11will be charge to a voltage equal to vbiasTX (node 6) which is typicallyset to ground: 0V. This is the reset phase. Once this ‘reset’ operationis completed, Node 5 is being set to 2.8V to turn off the resettransistor Mrt (1). In doing so, charge injection and parasiticcapacitive feedthrough effects will cause node 11, now becoming afloating node, to rise by approximately 300 mV. Therefore after the‘reset’ operation the actual ‘reset’ voltage value at node 11 isapproximately 0.3V.

At this time, the photo current s is being generated within Film (4),and the amount of photo current (photo sensitivity) generated isdependent on the voltage across the Film (4), i.e. (vsrc-vbiasR). WithvbiasR being able to be set arbitrarily to any voltage level from 0V to4V (generated through an on-chip charge-pump/regulator circuit), thelight sensitivity of the pixel can be adjusted.

The photo current from Film (4) charges up the parasitic capacitance atthe vsrc node (11) and its voltage level rises at a rate dependent onthe value of the parasitic capacitance at vsrc (node 11) as well as theequivalent conductance of the Film during the integration time.

After a specific integration time, the resulting integrated voltage atnode 11 will be read out through transistors Msf (2) and Mrs (3), thesource-follower buffer transistor and the Row-select transistor bysetting the node Sel (8) to ground.

T operation of this pixel is similar in principal to that of the 3T 2.4um NMOS pixel with all the transistors and voltage polarity ‘flipped’.The same technique can be used for all other embodiments of pixels asdescribed herein.

FIGS. 21-36 show additional pixel circuits including a “global” shutterarrangement. A global shutter arrangement allows a voltage for multiplepixels or the entire array of pixels to be captured at the same time. Inexample embodiments, these pixel circuits may be used in combinationwith small pixel regions that may have an area of less than 4micrometers squared and a distance between electrodes of less than 2micrometers in example embodiments. The pixel regions may be formed overthe semiconductor substrate and the pixel circuits may be formed on orin the substrate underneath the pixel regions. The pixel circuits may beelectrically connected to the electrodes of the pixel regions throughvias and interconnect layers of the integrated circuit. The metal layersmay be arranged to shield the pixel circuits (including transistors ordiodes used for global shutter) from light incident on the opticallysensitive layers in the pixel regions, as father described below.

Some embodiments of global shutter pixel circuits have a single globalshutter capture in which all of the rows are read out before a newintegration period is commenced. Other embodiments have a continuousglobal shutter that allows integration of a new frame to occursimultaneously with the read out of a previous frame. The maximum framerate is equal to the read out rate just as in the rolling shutter. Thesingle global shutter may require the read out to be stalled while thepixel integrates. Therefore, the maximum frame rate may be reduced bythe additional integration time.

Embodiments of global shutter pixel circuits described below includeseveral variations of 5T, 4T, 3T, 2T, and 1T pixels that achieve globalshutter using quantum dot film. In an example embodiment, the quantumdot film may be a photoconductor with an optically sensitive nanocrystalmaterial as described above. In example embodiments, the current acrossthe film has a non-linear relationship with light intensity absorbed bythe nanocrystal material. A bias is applied across the nanocrystalmaterial by electrodes as described above, which results in a voltagedifference across the film. In example embodiments, the film providesphotoconductive gain when this bias is applied across the film asdescribed above. The electrodes may be in any of the photoconductorconfigurations described above or in other configurations. In someembodiments, these circuit may be used to read out one layer of amulti-layer or multi-region color pixel as described further below.

In example embodiments of global shutter pixel circuits some or all ofthe following may be used:

-   -   The film can be configured as a current source or current sink    -   A charge store may be independent from the film in the pixel        region and isolated from the radiation source.    -   A separation element (including non-linear elements, e.g. a        diode or a switch) between the film interface and the storage        element may be used    -   A readout transistor, configured as an amplifier that may        operate independently of the other commonly connected devices        may be used. The amplifier is typically operated as a source        follower, but other embodiments may also be used.    -   Implicit or parasitic diodes that can be used to either reset        the film or control the readout transistor in some embodiments.    -   The array of pixel regions may have one common electrode shared        between all pixel regions (or sets of adjacent pixels) and each        pixel region may have one independent electrode isolated from        the others. The common electrode can be positive or negative and        does not have to be bound by CMOS rails or ESD devices in some        embodiments. The common electrode can accept dynamic signaling        in some embodiments.    -   For continuous shuttering with simultaneous readout, a mechanism        to reset the film independent from the charge store is used in        example embodiments.

The following FIGS. 21-26 illustrate global shutter pixel circuitsaccording to example embodiments. FIGS. 21-36A are each pixel schematiccircuit diagrams of a particular embodiment. Corresponding FIGS. 21-36Bare each device cross-section diagrams illustrating a physicalarrangement of the corresponding circuit in an integrated circuitdevice.

Abbreviations used to describe the various embodiments are explained asfollows: 4T indicates 4 transistors are used; C indicates “continuous”;NC indicates “non-continuous”; 2D indicates 2 diodes; and +1pD indicates1 parasitic (or essentially “free”) diode.

4T, NC Global Shutter Circuits:

The operating concept of the 4T is the basis for the other designs aswell. FIG. 21A is a circuit diagram of a pixel/cross-section/layout foran embodiment of a 4T, NC device 120. Device 120 is the isolation switchwhich enables the global shutter. The pixel is reset with RT high and Thigh. After the exposure expires, T is switched low and the film nolonger integrates onto the gate of 140. RS is switched high and INT issampled at CS.

Next RT and T are switched high and then low, in the appropriate order.The signal RESET is sampled. The pixel value is RESET-INT. The darklevel of the pixel is adjusted by setting CD to the desired value whichmay be different from the value of CD during global reset. Doublesampling serves the purpose of removing threshold variation and settingthe dark level offset. The film at 110 acts as a current sink Device 150acts as a switch for the source current for the follower at 140. Device130 resets the storage node and the film. The storage node is at 115.

5T, C Global Shutter Circuit:

FIG. 22A is a circuit diagram of a pixel/cross-section/layout for anembodiment of a 5T, C device. In order to achieve continuous globalshuttering shown in FIG. 22A, the film 210 is reset independently of thestorage element 215. The 5th transistor 221, as shown in FIG. 22Aenables this. The film with parasitics is then considered a selfcontained integrator. It is reset by 230 and charge is transferred with220. The sampling scheme is identical to the 4T design except for thefact that the storage element at 215 is now reset independently from thefilm, that is, signal T is low when RT is brought high.

4T (+1pD), C Global Shutter Circuit:

FIG. 23A is a variation of the circuit for the 4T as in FIG. 22A withthe addition of parasitics. These parasitics can be used to achievecontinuous global shuttering with only 4T in this embodiment. Theparasitic diode 312 now allows reset of the film 310. The common filmelectrode F is brought negative such that 312 turns on and resets thefilm to the desired level. This charges the parasitic film capacitor 311(not necessarily in the film). The F electrode is now brought back up toa new, higher level and the film is left to integrate. The film can nowbe reset as many times as desired without affecting the storage elementat 315.

4T (+1D), C Global Shutter Circuit:

Continuous shuttering shown in FIG. 24A is achieved in 4T with theaddition of a diode 411. The diode is created with a PN junction insidean Nwell region 485. The operation is the same as the 5T shown in FIG.22A. The main different is that the reset device is replaced with adiode. When RTF is high, current can flow to pull the film at 410 to thereset level. Later RTF falls to allow integration at the film node.Parasitic capacitance provides the primary storage node.

3T (+2D), C Global Shutter Circuit:

FIG. 25A shows a 3T configuration where diode 520 replaces thetransistor from 320. The parasitic diode 512 is used to reset the film510 independently of the storage node at the gate of 540. This isachieved by pulsing the F node to a negative value such that the diode512 turns on. After charge is integrated at 511, it is transferred bydriving F to a high voltage. This turns on diode 520.

2T (+2D), C Global Shutter Circuit:

FIG. 26A shows a 2T pixel capable of continuous global shuttering. The 2diodes at 612 and 620 act to reset the pixel and transfer charge asdescribed in section 6. Now the row select device at 550 is eliminated.The pixel works with a single column line 670 and a single row line 660.With the addition of the RT line, a total of 2 horizontal wires and 1vertical wire are needed for operation. This reduces the wiring loadnecessary for each pixel. The pixel works by resetting the storage nodeat the gate of 640 to a high voltage and then dropping R to the lowestvalue. This turns off the source follower at 640. In order to read thepixel, R is brought high. The parasitic capacitance at the pixel,particularly at Drain/Source of 630 causes the storage node to boost toa higher level as R is brought high. In this “winner-take-all”configuration, only the selected row will activate the column line.

3T (+1pD), C Global Shutter Circuit:

Another embodiment of the 3T continuous pixel is shown in FIG. 27A.Here, the row select device as described above is eliminated. Oneadvantage of this 3T is that there are no explicit diodes. The parasiticdiode at 712 resets the pixel independently from the storage node. Thecross section of the device in bulk 794 shows that a small layout ispossible.

1T (+3D) Global Shutter Circuit:

A 1T version of the pixel where diodes replace critical transistors isshown in FIG. 28A. First the film 810 is reset by bringing F negative.Next integrate by bringing F to an intermediate level. Finally, transfercharge by bringing F high. The scheme is such that even undersaturation, bringing F high pushes charge onto the storage node. Thestorage node is reset by bringing R low. Since charge is always pushedonto the storage node, we guarantee that the reset function properlysets the initial charge.

4T, PMOS Global Shutter Circuit:

A PMOS version of the 4T is shown in FIG. 29A. This operates similar tothe 4T NMOS version except that continuous shuttering is feasible withthe P+/NWell diodes 911. By bringing CD low enough, the film 910 resetthrough the diode to CD.

3T, PMOS Global Shutter Circuit:

A PMOS version of the 3T is shown in FIG. 30A. The row select device isnow eliminated and a compact layout is formed.

2T, PMOS Global Shutter Circuit:

A PMOS version of the 2T is shown in FIG. 31A. This works by resettingthe film globally by bringing CS low. Charge is then transferred across1120.

3T (+1D), NC Global Shutter Circuit:

FIG. 32A shows a 3T version of the pixel where the film 1210 sourcescurrent rather than sink it. The pixel integrates with F high. When F isforced low the diode 1220 turns off. Once the diode turns off, no morecharge is accumulated.

2T (+1D), NC Global Shutter Circuit:

FIG. 33A shows the 2T version where the row select device is eliminated.This saves some area from the 3T but reduces the pixel range.

2T (+1D) alt, NC Global Shutter Circuit:

FIG. 34A shows an alternative layout for the 2T where a diode is used asthe reset device.

2T (+1pD), NC Global Shutter Circuit:

FIG. 35A eliminates the reset device and makes use of the parasiticdiode 1512 to reset the film.

1T (+2D), NC Global Shutter Circuit:

The 1T with 2 diodes produces a compact layout as shown in FIG. 36A. Ifglobal shuttering is not needed, then it is possible to create a 1T with1 diode. The diode in this case is very small. This 1T+1D pixel removesthe diode 1620 between the film 1610 and the source follower gate 1640and makes a direct connection from the film to the source follower gate.The operation of this pixel can be deduced from the description of the1T+2D which follows. First reset the pixel by bring F high and R low.The film resets through the 2 diodes down to the low voltage at R (e.g.gnd). Next drive R to 1V. This causes the film to start integrating. Thevoltage at the source follower gate starts to increase. If the voltageincrease starts to exceed 1V, it will stay clamped by the voltage at R.This is the saturation level. For non-saturating pixel the gate willincrease in voltage by less than 1V. To stop integrating charge, F isdriven low. This cuts off the path for current to flow into the storagenode because of the diode action. When the pixel is to be read out, R isdriven up to 3V while the R at every other row is held at 1V. Thiscauses the storage element to boost in voltage by as much as 1V. Rprovides the drain current for the source follower and the column lineis driven by the activated row and no other rows because the sourcefollower is in a winner take all configuration. The INT value issampled. Next R is dropped to the low level and then pulled high again.This resets the storage node and then the RESET level is sampled. It ispossible to set a dark level offset by selecting the appropriate R levelin relation to the level used while resetting the film.

The above pixel circuits may be used with any of the photodetector andpixel region structures described above. In some embodiments, the abovepixel circuits may be used with multi-region pixel configurations byusing a pixel circuit for each region (such as a red, green and blueregions of optically sensitive material). The pixel circuit may read thesignals into a buffer that stores multiple color values for each pixel.For example, the array may read out the pixels on a row-by-row basis.The signals can then be converted to digital color pixel data. Thesepixel circuits are examples only and other embodiments may use othercircuits. In some embodiments, the film can be used in directintegration mode. Normally the film is treated as a photo-resistor thatchanges current or resistance with light level. In this directintegration mode, the film is biased to be a direct voltage outputdevice. The voltage level direct indicates the incident light level.

In some embodiments, the quantum film signal can be read out usingtransistors that have high noise factors. For example, thin oxidetransistors can be used to read out quantum film signal, with thepresence of large leakage current and other noise sources of thetransistors themselves. This becomes possible because the film hasintrinsic gain which helps suppress the transistor noise.

Electrical Interconnections 1404

Referring to FIG. 1, embodiments herein provide interconnection schemesbetween the quantum dot structures 1100 and the pixel circuitry 1700.The interconnections 1404 include systems and methods to take a signalfrom each layer of quantum dot material 200 and communicate it to thepixel circuitry 1700 (e.g. a transistor in the circuit). Embodimentsinvolve providing highly non-planar initial surface (i.e. posts ofvarying heights that will later connect to the appropriate layer ofquantum dot structure 1100). In embodiments, an interconnection may be aconductive post (e.g. metal posts) with insulator(s) at desiredlocations to prevent contact with layers that from which contact is notdesired. Nanoparticles may be deposited with a high degree of planarityover the non-planar substrate (i.e. they are planarizing). Connectionwith the electrical connections is achieved by flow of the nanoparticlesaround small objects such as posts during quantum dot application. Inembodiments, tungsten via levels are used, which are small compared tothe flow patterns of the quantum dot materials 200, and provide a gooddegree of uniformity around the electrical connections. The flowingquantum dot materials may provide a certain degree of planarization oversome length scale. Contact to the electrical interconnections isachieved with the aid of adhesion to the electrical interconnections1404. In embodiments, films are planarized following fabrication usingmethods such as chemo-mechanical polishing.

Embodiments may enable the addressing of multiple vertical layers ofelectrically-independent (or nearly-electrically-independent)photoconductive layers using a multiplicity of posts that contact thismaterial substantially from the side. Regions of each post may beelectrically conductive to enable electrical contact to the film; whileother regions are masked using an insulating layer such as an oxide ornitride to avoid contacting layers to which electrical contact by theseposts is not desired. In embodiments, these contacting posts may beformed using vias formed in prior CMOS process layers. In embodiments,the insulating layer or layers protecting the vias may be selectivelyetched to reveal portions of the via for electrical contacting to asubsequently-deposited photoconductive layer. In embodiments, selectiveetching of the insulating material only may result in a layer of exposedvia metal posts. These may then be covered using a conformal coating ofa subsequently-deposited insulating layer. This may result in exposing aportion of each metal post, such as the top, while leaving the sidesprotected. In this embodiment, the sidewalls are protected, while thetops are open and available for electrical contact. In this embodiment,those posts that have been used to contact lower layers may be used toprovide electrical access to a dark (or darker) reference. Those metalposts that are only deprotected on top instead contact an upper layerwhich forms the strongly-illuminated top pixel. In embodiments, insteadof providing independently-addressed light pixels with dark referencesbeneath, the same method of selective deprotection and contacting ofdifferent vertically-stacked pixel layers may be employed to addressdifferently spectrally-sensitive (e.g. color) stacked pixels.

In embodiments, quantum dot materials 200 may be electricallyinterconnected 1404 to pixel circuitry 1700 utilizing a plurality ofcontact configurations, such as in a lateral planar structure 1418, avertical stacked structure 1420, a combination of planar and verticalstructures, or the like, as shown in FIG. 3. In the lateral planarstructure 1418 metal contacts 1412 are laid out in the same layer of thephotodetector structure 1400, in this case on top of a glass substrate1414 and overlaid with the quantum dot material 200. In a similarlateral planar structure 1418, the metal contacts 1412 could have beenlaid on top of the quantum dot material 200. In a vertical stackedstructure 1420 metal contacts 1412 are laid out in different layers ofthe photodetector structure 1400, in this case with a metal contactbetween the glass substrate 1414 and the quantum dot material 200, and atransparent contact such as ITO on top of the quantum dot material 200.In embodiments, the electrical connections 1412 are a variety ofelectrical interconnections 1404, and may be one or more of a pluralityof different conductors, such as gold, aluminum, tungsten, copper,tantalum titride (TaN), titanium nitride (TiN), Indium, Aluminum cappedwith TaN or TiN, or the like. These configurations represent only two ofa plurality of possible electrical interconnection 1404 contactconfigurations, and other configurations will be obvious to one skilledin the art.

An aspect of the present embodiments relates to the layout of the metalcontacts relative to the semiconductor photodetector. The electricalinterconnections 1404 relate to flow of electricity in severaldirections. Flow directions generally involve vertical structures (i.e.predominantly up-down current flow) or lateral structures (i.e. planararchitecture devices with lateral current flow) or combinations ofvertical and lateral structures (i.e. control element in verticaldimension and current flow in lateral dimension or build up lateralstructures in a vertical dimension-monolithic integration in thevertical axis).

An aspect of the present embodiments relates to pattern of contacts. Inembodiments there may be a lateral presentation of contacts. Forexample, a row of five along two edges of a square with one bias, anarray of edges with ground and positive voltage in the middle, aserpentine pattern, etc. Within one pixel, the system could ground atthe bottom of a column and bias at the top of the next column. Thepattern could be serpentine, discretized serpentine, interspersed, etc.In embodiments squares can be filled in with circles that lead to usefulbiasing regimes. For example a plus/minus checkerboard (equivalent todiagonal rows) could be useful. Another pattern could be fill factordimension: filling in space from a bird's eye view of the pixel. Thecontacts may be co-planar. With respect to the percentage area that iscovered metal from above, one might want to minimize it or one might notwant to minimize (e.g., maximize to increase reflectance—thickness isless but still get all radiation 1000 and same quantum efficiency).There may be implications such as making a film of medium thicknessrelative to the absorption length, conductance versus depth throughmaterial, conductance contour versus spatial dimension, current went upfrom one contact and then down to the other. In embodiments, thedimension is small, surface conductivity is large and routing of currentflow from contact to contact may mean fill factor cannot be reduced; theless-illuminated dimension is to be smaller than the lateral dimensionto provide this.

In embodiments intentionally induced cracking in the film could producesub-critical dimension breaks in the film (e.g. cracks where the metalbounds the cracks). In this instance, surface preparation may affect thecrack propagation. Embodiments may involve putting down metal patterns,such as in pentagons, hexagons, squares, or the like, and then layeringfilm onto the metal. When processed the film may form cracks, producingan electrical isolation between parts. In embodiments, the cracks may beself-aligned along the metal patterns, or there may be a patterned metaltemplate where there is a minimum dimension gap between the patternedmetal regions. In embodiments, a material, such as ITO or similarmaterial, could be applied into the cracks formed in the gaps

The electrical interconnections may be made of a variety of metals. Themetals may form the contacts to the quantum dot structures 1100. In thecase of lateral devices, they may constitute the electrodes. In verticaldevices, they may be the bread of a vertical sandwich and the quantumdot structures 1100 are the middle layer. In embodiments the metals maybe Pt, Au, Ni, tungsten, aluminum, copper, gold, TaN (tantalum nitride),TiN (titanium nitride), indium, aluminum capped with TaN or TiN or othersuitable material.

Embodiments involve a planar architecture shape for the electricalinterconnects with a four-point probe architecture. It may use outerpair of contacts to apply a positive voltage bias and to read currentflows or resistance changes. In an alternate embodiment, theconfiguration may have an inner biased pair that is used to measure. Thearrangement could include electrical interconnects formed by dots,lines, rings, circles, squares, etc. The electrical interconnects may beprovided and this may involve tiling the interconnects in different ways(e.g. hexagonal, fractal tilings, column pitch, etc.). This may providea fundamental advantage from a space perspective. A four-point probearchitecture may involve the use of an outer pair of contacts to applyvoltage bias and an inner pair for measurements. Each electrode could beaddressed off chip. Embodiments involve a variety of electricalinterconnect patterns: hexagonal, fractal, column pitch, rows/columns,hexagonal, or others and there may be various groups, they may bedistributed beneath array, and these things may provide increasedflexibility by decoupling array from circuitry.

There may be a degree of planarity (pre and post-quantum dot structureaddition) associated with the layout of the electrical interconnects offocal plane arrays. Embodiments may provide electrical interconnectsthat are polished (e.g. so the tops aligned with a passivation layer).The electrical interconnects could have plugs of metal sticking up abovethe planar level (e.g. this could be desirable in order to enabledifferent degrees in stacked architectures). The electricalinterconnects could have valleys in metal and the valleys may be filledin with a material to provide an internally dark region. A darkreference electrical interconnect may be provided internal to the mainelectrical interconnect to make a dark reference measurement. They couldhave a valley, which could bring radiation 1000 in, propagate and bringradiation 1000 back out again. They could have a lateral structure.Embodiments may have dielectrics that could bring the metal out,involving the building of an interference filter out of the layers.Embodiments may involve an intentionally sacrificial layer (e.g., ofmetal) that may enable a spectral shaping allowing a flattening of thegain curve (e.g. such as for enhanced red response, etc.). Embodimentsmay involve making a six-layer interference coating and manipulatingthicknesses of the layers to change the spectral response (such as toboost red response, or blue response, etc.).

Before applying the quantum dot structures 1100 the electricalinterconnections 1404 may be formed. The interconnections may comepolished and have its tops aligned with passivation outside. It mayinvolve plugs of metal sticking up above planar level and this mayenabling stacked architectures. There may be valleys in metal and theremay be fill in materials and have dark references where material isblocked by absorption of radiation 1000. The valleys may bring radiation1000 in, propagate and bring radiation 1000 back out again. Theinterconnections may include dielectrics that bring the metal out. Anembodiment may be an interference filter and the interference filter maybe a six layer interference coating where moves may be made around incolor by changing the thickness of the layers. This may be used to boostred response, boost blue response or alter other spectral properties.Embodiments may include a sacrificial layer (e.g., of the metal) in eachof the right places. This may involve spectral shaping (e.g. to flattenthe gain curve), which may be used to alter a spectral response (e.g.enhanced red response).

In embodiments the optical properties of the pixel may be altered by thematerials and processing between silicon base and the quantum dotstructures 1100. The optical properties may be reflectance, spectralcharacteristics, directional properties (e.g. normal and cavity) andcreating scattering structures (e.g. scatter to film to increase pathlength).

Following the application of the quantum dot structures 1100 thematerials may be put through a process to smooth, roughen, causespecular/reflecting properties, cause scattering properties (e.g. affectchief ray angle), alter the refractive index of the quantum dotstructures 1100, alter index matching (e.g. influence internal ray anglewhich has implications for cross-talk), make viscosity adjustments orthe like.

In embodiments, a passivation layer is provided on top of thephotosensitive quantum dot structure 1100. The passivation layer mayensure that there are not undesired changes in photosensitive layerproperties owing to interdiffusion among the materials making up thephotosensitive layer. The passivation layers may be stoichiometricallymatched, in at least one chemical constituent, to the quantum dotstructure layer 1100 on which it is provided. For example, PbS may bepassivated using As2S3 (arsenic trisulfide), in view of the matching ofthe sulfur compounds in the active layer and the passivation layer. Inembodiments the passivation layer(s) may be used for encapsulation toensure that substantially no molecules contained in the environmentabove the chip's top surface penetrate into the region in which thephotosensitive layer and its associated materials (e.g. the quantum dotstructure layer 1100) reside; and, similarly, that atoms or moleculesassociated with the operation of the photosensitive device don't escapefrom the region in which the device is contained. These encapsulationlayers contribute to ensuring that the device is substantially unchangedin its performance over the product's lifetime. In embodiments thepassivation layer(s) may be used for compatibilization to ensure that,following processing of the photosensitive material (e.g. the quantumdot structures 1100), the chip may be returned into a conventionalcommercial fabrication facility, for example for the subsequentincorporation of color filter arrays, and/or for the subsequentrealization of camera modules. A compatibilization layer includes forexample Si3N4, silicon nitride. Foundries are acquainted with theprocessing of substrates which are Si3N4-capped; thus the layer canserve as compatibilization layer. In embodiments the compatibilizationand encapsulation layers may be one and the same if a single layer, orlayer structure, simultaneously serves both purposes.

In embodiments other layers are included for index-matching of thephotosensitive layer or ancillary layers (e.g. passivation,encapsulation, compatibilization), color-filters for implementing colorfilter arrays, and passivation of the color-filter arrays.

Embodiments may also include layers for the purpose of increasing thescattering of radiation 1000. These scattering layers, instead of beingindex-matching, provide a significant index mismatch between layersabove and/or below. Their purpose may be to increase the absorbance ofradiation 1000 by providing photons with repeated possibilities oftraveling through the photosensitive layer, thereby increase absorbancefor a given thickness of absorbing material.

FIG. 3 a illustrates an electrical interconnection according toprinciples of the present embodiment. In this embodiment, conductiveposts 1404 are provided in connection with a supporting substrate 1410.The 1410 post may have an insulating material on the outer surface toprevent electrical conductivity with unwanted portions of the device.The post 1410 may also have a section (e.g. at the top of the post) thathas an exposed conductive layer such that it can electrically connectwith the quantum dot structures 1100 (depicted as the various regions inFIG. 3 a). In this embodiment, posts of varying heights are providedsuch that each one electrically connects with at least one of the activelayers of the device. In embodiments, the post has an electricallyexposed portion at a position other than at the top (e.g. at somemid-point). This may be to facilitate electrical connection with one ofthe mid-level regions (e.g. to provide many posts of similar height butfor various active layers). The posts generally have an exposedelectrical region at the bottom (e.g. the substrate end) to makeelectrical connection with circuitry (e.g. pixel circuitry or a chipprocessor).

In embodiments several quantum dot structures 1100 will be layered ontop of one another (e.g. through several spin-coatings as describedherein) to form a multi-layered quantum dot structure 1100, as describedabove. The multi-layered quantum dot structure may include layers ofsimilar quantum dot materials or different quantum dot materials asdescribed herein (e.g. two different color receptors may be used in thetwo separate layers). The total stack height may be approximately onemicron with a lateral dimension of approximately two microns. Inembodiments, the two layers may communicate with one another throughtheir electrical interconnections. The layers may be provided withinsulating properties to prevent such communications. For example, avery thin 1000 angstrom dielectric layer may be applied between theseparate quantum dot structures 1100. In the manufacturing process, thetops of vertical electrical interconnectors (e.g. posts) may have to becleaned to expose an electrically conductive area after the dielectriclayer is applied. In embodiments, the dielectric is sin coated onto asub-layer of quantum dot material and then a light etch is applied toclean the top of the posts to remove the dielectric and to expose theelectrically conductive area such that it can communicate electriccharges from a quantum dot structure laying on top of the dielectriclayer. In another embodiment, the vertical electrical interconnections(e.g. posts) are not coated with dielectric material during thedielectric material coating process. This may be achieved by masking theelectrical interconnects during the dielectric coating process, forexample.

In embodiments, there may be a known, measurable or assumed level ofcrosstalk between the separate layers of quantum dot structures 1100.The crosstalk may be the result of a lack of dielectric between thelayers, imperfect application of a dielectric layer, over-etching orcleaning of certain areas (e.g. over-etching the dielectric around theposts and creating electrical contact areas at the posts between thelayers) or for other reasons. In embodiments compensations oradjustments may be made due to the crosstalk. For example, the pixelcircuitry 1700 may be used to alter the signal that is received from thequantum dot structures 1100 and/or the chip processor 2008 may be usedto make such compensations.

FIG. 3 g illustrates a quantum dot structure 1100 stack involving twoseparate layers of quantum dot materials 1100 and a layer of dielectricmaterial 1460 between the two separate layers of quantum dot materials1100. A vertical electrical interconnect in the form of a post isprovided. The post includes an outer layer of dielectric material 1460and in inner layer of electrically conductive material 1470. The innerlayer of conductive material 1470 is exposed at the top, in thisembodiment, to form an electrical interconnection with the top layer ofquantum dot structure 1100. In other embodiments, the inner conductivelayer 1470 may be exposed at an intermediate location on the post toform an electrical interconnection with another corresponding layer. Abottom portion of the inner conductive material of the post may also beexposed to facilitate electrical communication with other circuitry(e.g. pixel circuitry 1700 and/or chip processor 2008).

In embodiments, the QDPC 100 may combine a plurality of different pixellayouts 1600, electrical interconnections 1404, and pixel circuitry1700, as discussed herein, in the implementation of an image sensor. Asan illustration of how these elements may interrelate, FIG. 3 h providesone example of a multi-layered quantum dot structure 1480, withelectrical interconnections 1450 and 1452, pixel circuitry 1700 andpixel assignment 1482. FIG. 3 h provides a single illustrating example,and is not meant to be limiting with regard to the plurality of planarinterconnection, vertical interconnection, pixel layout 1600, and darkpixel layouts discussed herein.

Referring to the specific example provided in FIG. 3 h, the multilayeredquantum dot structure 1480 is shown to include two separate quantum dotstructure layers 1100 with a dielectric layer 1460 between the twoquantum dot structure layers to provide electrical isolation between theactive layers. As discussed elsewhere herein, embodiments of amulti-layered stack of quantum dot structures 1480 may not require thedielectric layer 1460. A photodetecting quantum dot pixel segment 1484Aand a dark quantum dot pixel segment 1488A are shown located within thefirst quantum dot structure layer 1100A. In this embodiment, thephotodetecting quantum dot pixel segment 1484A is located proximate tothe top surface layer of the first quantum dot structure layer 1100A,and the dark quantum dot pixel segment 1488A is located proximate to thebottom of the first quantum dot structure layer 1100A. With thisarrangement, the photodetecting quantum dot segments, including segment1484A, are positioned near the most active region of the quantum dotstructure 1100A so they can pick up signal changes in the structure 1100that are due to radiation 1000 falling on the structure's surface.

A matrix of photodetecting segments may be provided across a surface ofthe structure 1100 such that incident radiation 1000 on the surface canbe addressed and read out. The dark quantum dot pixel segment 1488A ispositioned proximate the bottom of the structure so it is shielded fromthe most active portions of the structure so it can be used to make darkmeasurements as described elsewhere herein. As discussed elsewhereherein, the dark quantum dot pixel segment may be positioned at otherpoints within the photoconductive structure or in another location.

The quantum dot pixel structures 1484 may be constructed using planarelectrical interconnections as described herein (e.g. such as thosedescribed in connection with FIGS. 3 b-3 e). These planar electricalinterconnection structures may be in a plane substantially parallel withthe incident radiation 1000 plane, as indicated in FIG. 3 h. Verticalelectrical interconnections may be associated with the planarinterconnections at one end and pixel circuitry 1700 at the other tobring the signal to the pixel circuitry, and/or measure resistance orother electrical property of the quantum dot pixel structure 1100. Inthis embodiment, a simple-closed planar electrical interconnection isshown and the simple closed planar electrical interconnection has itscenter electrical connection 1452 held at a positive bias and its outersquare ring electrical interconnection 1450 used as a ground plane.

Each pixel segment 1484 is associated with its own positively biasedelectrical interconnection 1452 and its own or a common ground planeelectrical interconnection 1450. When radiation 1000B, to whichstructure 1100A is responsive, strikes the photodetecting quantum dotpixel segment 1484A, electron-hole pairs are created in the pixelsegment 1484A, and caused to flow due to the associated positivelybiased electrical interconnection 1452. While only four photodetectingquantum dot pixel segments are shown as associated with an upper surfaceof the quantum dot structure 1100A, it should be understood that this isfor simplification in providing this explanation and that it isenvisioned that such an electrical interconnection pattern would bereplicated many times across the upper surface of the quantum dot pixelstructure 1100A. Similarly, only one dark quantum dot pixel segment1488A is shown with respect to the structure 1100A; however, there couldbe many such dark segments and the dark segments may be associated withother layers.

The second quantum dot structure 1100B is illustrated with electricalinterconnections that are similar to that of the first quantum dotstructure 1100A. The second structure 1100B has a matrix ofphotodetecting quantum dot pixel segments, including segment 1484B, anda dark quantum dot pixel segment 1488B. This arrangement is similar inconstruction in this illustration but it should be understood that thesecond layer 1100B could have a different configuration. For example,one of the other illustrated planar electrical interconnection schemescould be provided on the second layer 1100B. However, for simplificationof the explanation, a similar construction has been presented. Generallyspeaking, the second layer 1100B is adapted to respond to a differentwavelength of radiation as compared to the first layer 1100A to form amulti-spectral system. For example, the photodetecting quantum dot pixelsegment 1484B may include quantum dots that are responsive to red lightwhile the photodetecting quantum dot pixel segment 1484A may includequantum dots that are responsive to blue light. The red light would betransmitted through the first layer 1100A to the second layer 1100Bwhere the second layer 1100B would develop an electrical signal and readby the matrix of electrical interconnections. This electrical signalwould then be processed in turn by the associated pixel circuitry suchthat it could be quantified and located.

In embodiments, the electrical interconnections 1450 and 1452 of aquantum dot pixel segments 1484 and 1488 may have a plurality ofdifferent layouts or configurations. FIG. 3 h shows a layout similar tothe simple-closed layouts of 1430 and 1432 of FIG. 3 b, where oneelectrical interconnect 1450 is configured as a rectangle around thepixel segment area where the effective area of the pixel segment isdefined by the rectangle. Although FIG. 3 h shows this particularelectrical interconnection configuration, it is understood that this isonly for explanatory purposes, and does not limit the configuration toany of the plurality of configurations that are encompassed by thepresent embodiment.

Continuing to refer to the multi-layered stack of quantum dot structures1480 in FIG. 3 h, a pixel assignment 1482 may be made by selecting oneor more photodetecting quantum dot pixel segments 1484 to be included ina pixel definition. For example, pixel segment 1484A and 1484B may beselected to form a pixel. When pixel segment 1484A responds to radiation1000 that it receives, the segment will generate an electrical signalthat flows in response to pixel segment's associated positively biasedelectrical interconnection 1452. The associated pixel circuitry may theninterpret the signal (e.g. by measuring a resistance change to estimatethe amount of incident radiation 1000). This may result in a first pixelsegment radiation 1000 contribution. Since the type of quantum dotstructure that makes up the layer 1100A in known, this segment radiation1000 contribution can be attributed to a particular wavelength ofradiation 1000. At substantially the same time that the first pixelsegment radiation 1000 contribution is determined, a second radiation1000 contribution may be determined by monitoring the pixel circuitryassociated with pixel segment 1484B. If radiation 1000 to which thestructure 1100B has been received by pixel segment 1484B, then signalwill be read via the interconnection 1452 that is associated with thepixel segment 1484B so the pixel circuitry can read the activity. Theactivity readings from the two pixel segments 1484A and 1484B may thenbe combined per an assignment protocol. As will be appreciated, anynumber of pixels segments could be combined to form a pixel.

When the pixel circuitry 1700 determines the amount of resistance changeor incident radiation 1000 fallen on a pixel segment 1484, it may takeinto account a dark reading obtained from one or more of the dark pixelsegments 1488. For example, when a resistance change is interpreted bypixel circuitry associated with pixel segment 1484B, the resistancechange associated with dark pixel segment 1488B may be interpreted. Ifthe dark pixel 1488B shows a change of equal magnitude to the activepixel segment 1488A, a determination may be made that no radiation 1000was received by the active pixel segment 1488A. Similarly, the darkreference may be used to subtract an amount representing noise from theactive signal, or other such compensation algorithms may be applied.

In embodiments, regions of a photoconductive layer are electricallycontacted by an array of electrodes. It is important to achieveconsistent, robust mechanical and electrical contact between thephotoconductive layer and the electrical contacts. Following fabricationof the electrical contacts, there may exist residual oxides,oxynitrides, or organic materials. In embodiments, it may be importantto remove the organic materials; this may be accomplished using anoxygen plasma etch, an acid-alkaline clean, an alkaline-acid clean, orcombinations thereof. In embodiments, it may be important to remove theoxides and/or the oxynitrides; this may be accomplished using a dry etchor a wet etch. thin barrier layer atop the electrical contacts, prior tothe deposition of the photoconductive layer.

In embodiments, it may be important to achieve electrical contactthrough a thin barrier layer between the electrical contacts mentionedabove and the photoconductive layer. In this instance, it is importantto remove oxides, oxynitrides, and/or organic materials of unknown oruncontrolled thickness; and then to deposit, or otherwise form, acontrolled thin barrier layer atop the electrical contacts, prior to thedeposition of the photoconductive layer.

In embodiments, in order to achieve robust mechanical and electricalcontact of the photoconductive layer to the electrical contacts, anadhesion material may be employed. This material may include a moietyhaving an affinity to the materials at the surface of the electricalcontacts, and another moiety having an affinity to the materials at thesurface of the constituents of the photoconductive layer. As oneexample, if the electrical contacts are terminated with TiN (titaniumnitride) or an oxynitride thereof, then one moiety in the adhesion layermay be an amine functional group. As another example, if thephotoconductive layer includes a metal such as Pb, Cd, Cu, In, or Bi,then one moiety in the adhesion layer may be a thiol functional group.Such an adhesion, or anchor, layer may be applied by spin-casting,dip-coating prior to, during, or following deposition of some or all ofthe photoconductive layer.

In embodiments, electrical contacts having a deep work function areused, as described in detail herein. Deep work function is used hereinto include a work function lower than 4.4 eV or 4.6 eV or 4.8 eV belowthe vacuum level. If a binary alloy such as TiN (titanium nitride) isemployed, the work function may be deepened by controlling the ratio ofTi to N during formation of the alloy. For example, a high ratio(greater than 1:1) of N to Ti may be used.

In embodiments, electrical contacts work function may be influencedthrough control over the incorporation of oxygen. Ternary alloys such asTiOxNy (titanium oxynitride) may be employed, and the work function maythereby be determined by the ratio of O to N. For example, the use of ahigher ratio of O to N may be employed.

In embodiments, electrical contacts having a specific work function maybe desired. The work function of an already-patterned set of electricalcontacts may be modified by first depositing a thin layer of anothermaterial, such as, for example, a 10 nm layer of Au, Pd, Pt, or Ni; andthe continuity of this deposited layer may then be deliberatelydisrupted using a selective lift-off technique wherein deposited metalscovering a region where the metals are not desired are lifted offthrough selective etching of the non-contacting material (e.g. bufferedoxide etching of an oxide in the non-contacting regions).

In embodiments, electrical contacts having a specific work function maybe desired. The work function of an already-patterned set of electricalcontacts may be modified by (1) treating the sample, throughspin-coating, dip-coating, spray-coating, or other method, with amaterial that adheres selectively to materials over which electricalcontact is not desired; (2) depositing a thin layer of another material,such as, for example, a 10 nm layer of Au, Pd, Pt, or Ni; and (3) thencleaning the wafer to lift off the deposited layer in regions wherecontact is not desired.

Integration of combinations of the various quantum dot structures,pixels, interconnects, and circuitry, as described above, results in anintegrated circuit (IC), under an embodiment. FIG. 9 is a diagrammaticillustration of a scanning electron micrograph of an integrated circuitin which an optically sensitive film has been spin-coated onto a CMOSintegrated circuit produced in a CMOS foundry, under an embodiment. Theoptically sensitive film of this example includes PbS colloidal quantumdots possessing a substantially single-time-constant trap stateresulting from the presence of PbSO3 on their surface. The depictedcomponents of the integrated circuit, individually described in detailherein, are now described in detail.

Layer 101 is silicon as the semiconductor substrate on which theintegrated circuit is formed. Various impurities have been implantedand/or annealed into the substrate to form diodes, transistors, wells,resistive/conductive regions, and the like. Layer 102 is the transistorand gate level and contacts. Material such as poly-silicon, dielectric,and metals are incorporated in these layers in order to form a varietyof electronic devices enabling electronic circuit realization.

Layers 103, 104, 106, 108, 110 each include metals providinginterconnection in the substrate-plane among transistors and othercircuit elements on the integrated circuit. Layers 105, 107, 109, 111are vias providing interconnection perpendicular to the substrate-planeamong the various metal layers.

Layer 112 is the top metal layer. It provides electric contact with theoptically sensitive layer (Layer 113) made using PbS colloidal quantumdots. In this example, an optically sensitive layer conformally coatsthe top metal. Although the top surface of the substrate prior todeposition of the optically sensitive layer is not completely planar(˜100 nm surface height variation), the top surface of the opticallysensitive layer is substantially planar (<10 nm surface heightvariation) owing to the planarizing properties of the particular processemployed.

Layer 114 is an encapsulation layer that encapsulates the opticallysensitive layer (Layer 113). The purpose of the encapsulation layer, inan embodiment, includes the avoidance of interdiffusion with subsequentlayers (e.g., color filter arrays, microlenses, wafer-level optics,etc.) and also the prevention of penetration into the opticallysensitive layer (Layer 113) by gases such as H2O, O2, CO2, and liquidssuch as H2O and organic solvent used in subsequent processing. Layers115 and 116 are thin metal layers.

FIG. 10 illustrates four process flows (a, b, c, and d) that can be usedto produce integrated circuits similar to those shown in FIG. 9 anddescribed herein. The four process flows of an embodiment include, butare not limited to, a blanket etch process, a masked step etch process,a first pure TiN process, and a second pure TiN process, each of whichis described in turn.

FIG. 10( a) shows the blanket etch process flow, under an embodiment.Blanket Etch describes a means of producing a substantially planar topcontact layer (top of layer 112 (e.g., Metal 6) in FIG. 9). In thisillustration, the top contact layer will provide pixelated electricalcontact to the optically sensitive layer, and will also provide for bondpads for electrical communication with optical system elements off-chip(power, control and data in/out). In step 1, the material that willultimately serve as top metal, a stack consisting in this example of TiNfollowed by Al followed by TiN, is deposited. In step 2, photoresist isapplied and lithographically patterned. In step 3, a dry etch isemployed to etch the regions unprotected by photoresist and thustransfer the photoresist's pattern to the TiN/Al/TiN stack beneath. Instep 4, a passivating oxide is deposited, and in step 5, it ischemomechanically polished to produce a smooth top surface of a desiredthickness. In step 6, a blanket etch is employed to etch completelythrough the thickness of passivation oxide residing above the patternedTiN/Al/TiN, thus exposing at a minimum the top surface of the TiN in thestack. In step 7, an alloying process is employed to complete theprocess flow.

FIG. 10( b) shows the masked step etch process flow, under anembodiment. Masked step etch describes a means of producing a topcontact layer (top of layer 112 (e.g., Metal 6) in FIG. 9) in whichsubstantially only the region that will form the image sensor array, andthe regions that will form bond pads, become exposed via removal ofpassivation oxide. In this illustration, the top contact layer willprovide pixelated electrical contact to the optically sensitive layer,and will also provide for bond pads for electrical communication withoptical system elements off-chip (power, control and data in/out). Instep 1, the material that will ultimately serve as top metal, a stackconsisting in this example of TiN followed by Al followed by TiN, isdeposited. In step 2, photoresist is applied and lithographicallypatterned. In step 3, a dry etch is employed to etch the regionsunprotected by photoresist and thus transfer the photoresist's patternto the TiN/Al/TiN stack beneath. In step 4, a passivating oxide isdeposited, and in step 5, it is chemomechanically polished to produce asmooth top surface of a desired thickness. In step 6, photoresist isapplied and lithographically patterned to expose the area of the imagingarea and the bond pads. In step 7 a first etch of thephotoresist-patterned wafer is employed to remove some, but not all, ofthe passivation oxide covering the pixel electrodes and bond pads. Instep 8, the photoresist mask is stripped. In step 9, the entire wafer isetched, revealing the pixel electrodes and bond pads as a result of theprior patterned etching step. In step 10, an alloying process isemployed to complete the process flow.

FIG. 10( c) shows the first pure TiN process flow, under an embodiment.Pure TiN describes a means of producing a top contact layer (top oflayer 112 (e.g., Metal 6) in FIG. 9) in which substantially only theregion that will form the image sensor array, and the regions that willform bond pads, become exposed via removal of passivation oxide. In thisillustration, the top contact layer will provide pixelated electricalcontact to the optically sensitive layer, and will also provide for bondpads for electrical communication with optical system elements off-chip(power, control and data in/out). In step 1, the material that willultimately serve as top metal, TiN, is deposited. In step 2, photoresistis applied and lithographically patterned. In step 3, a dry etch isemployed to etch the regions unprotected by photoresist and thustransfer the photoresist's pattern to the TiN. In step 4, an alloyingprocess is employed to complete the process flow.

FIG. 10( d) shows the second pure TiN process flow, under an embodiment.The second pure TiN process describes a means of producing a top contactlayer (top of layer 112 (e.g., Metal 6) in FIG. 9) in whichsubstantially only the region that will form the image sensor array, andthe regions that will form bond pads, become exposed via removal ofpassivation oxide. In this illustration, the top contact layer willprovide pixelated electrical contact to the optically sensitive layer,and will also provide for bond pads for electrical communication withoptical system elements off-chip (power, control and data in/out). Instep 1, the material that will ultimately serve as top metal, TiN, isdeposited. The wafer presented prior to this deposition provides W(tungsten) vias for pixel electrodes, but does not provide W (tungsten)contacts to the regions where bondpads will subsequently be formed. Instep 2, photoresist is applied and lithographically patterned: regionswhere TiN is to remain, and thus which will electrically contact theoptically sensitive layer, are protected, while all other regions(including those residing above future bond pads) are exposed. In step3, a dry etch is employed to etch the regions unprotected by photoresistand thus transfer the photoresist's pattern to the TiN. In step 4,photoresist is applied and lithographically patterned: regions in whichphotoresist is absent following patterning define what will laterconstitute bondpads. In step 5, the oxide protecting the bondpad inMetal 5 is opened via a dry etch. In step 6, the photoresist is removed.In step 7, an alloying process is employed to complete the process flow.

FIG. 11 shows a scanning electron micrograph of an integrated circuit inwhich an optically sensitive film has been spin-coated onto a CMOSintegrated circuit produced in a CMOS foundry, under an alternativeembodiment. In this alternative embodiment, metal layer 112 is notpresent, but thin coating layers 115 and 166 are present.

In general, FIGS. 9-11 are illustrations of an optoelectronic devicecomprising an optically sensitive layer; a CMOS integrated circuitcomprising a silicon substrate, at least one diffusion layer, at leastone polysilicon layer and at least two metal interconnect layers,including at least a first metal layer and a second metal layer; anoptically sensitive layer in electrical communication with the secondmetal layer; wherein the at least one polysilicon layer and the at leastone diffusion layer forming a plurality of transistors in electricalcommunication with the optically sensitive layer through at least thesecond metal layer.

In embodiments, the thickness of the top electrode is in the range 10-50nm, whereas the lateral dimensions of the top electrode are in the range200-400 nm, and thus the width:height aspect ratio of the top electrodeis in the range 40:1 to 4:1. In embodiments, the use of a thin topelectrode in the range 10-50 nm provides a simplified means of realizinga substantially planar (surface height variation less than 100 nm) topsurface of the wafer prior to application of the optically sensitivelayer.

In embodiments, TiN of thickness 10-50 nm is used as the top electrodewhich is in electrical communication with the optically sensitive layer.In other embodiments, TiN of thickness 10-40 nm capped with TiOxNy ofthickness 2-20 nm is used as the top electrode which is in electricalcommunication with the optically sensitive layer.

In embodiments, the top metal level includes TiN but excludes Aluminum.In embodiments, the etching of the top electrode in order to form alateral pattern may avoid the generation of aluminum oxides and relatedmaterials by avoiding the use of aluminum as part of the top-metalcomposition.

In embodiments, the top electrode may include platinum (Pt), adeep-work-function noble metal known to provide for consistency ofcontact, including ohmic contact to the valence band of PbS colloidalquantum dot films. The use of such a top electrode may also provide adegree of blocking of electron injection into, or electron escape from,the optically sensitive layer in view of an energetic barrier formed atand near the contact-to-optically-sensitive-layer interface.

In embodiments, the top electrode may include palladium (Pd), adeep-work-function noble metal known to provide for consistency ofcontact, including ohmic contact to the valence band of PbS colloidalquantum dot films. The use of such a top electrode may also provide adegree of blocking of electron injection into, or electron escape from,the optically sensitive layer in view of an energetic barrier formed atand near the contact-to-optically-sensitive-layer interface.

In embodiments, the top electrode may include gold (Au), adeep-work-function noble metal known to provide for consistency ofcontact, including ohmic contact to the valence band of PbS colloidalquantum dot films. The use of such a top electrode may also provide adegree of blocking of electron injection into, or electron escape from,the optically sensitive layer in view of an energetic barrier formed atand near the contact-to-optically-sensitive-layer interface.

In embodiments, the top electrode may employ indium tin oxide (ITO), asubstantially transparent conductive oxide that provides electricalcontact to PbS colloidal quantum dot films. In embodiments, the topelectrode may include zinc oxide (ZnO), a substantially transparentconductive oxide that provides electrical contact to PbS colloidalquantum dot films.

In embodiments, the top electrode may employ a stack of materials suchas, but not limited to, the following: TiN/Al/TiN with constituent X;TiN with constituent X; TaN with constituent X; Ni with constituent X;and, Cu with constituent X. Constituent X includes any of Pt, Pd, Au,ITO, or ZnO. In consideration of the above material combinations for thetop electrode, thicknesses of the top electrode include, but are notlimited to, the following: 10-50 nm thickness for TiN, TaN, Ni, Cu; 2-50nm thickness for Pt, Pd, Au; and, 5-100 nm thickness for ITO, ZnO, orother conductive oxides.

Thus, in general, multilayer contacts may be provided according to theteachings herein in which a variety of metals and/or other conductivematerials are in physical contact. For example, W may be used as a viametal; TiN may be used to protect that via; and a deep-work-functionmetal may be contacted to the TiN in order to provide adeep-work-function electrical connection to the optically sensitivelayer.

As described above, metal and/or metal contacts in a vertical stackedstructure can be laid out in different layers of the photodetectorstructure and used as contacts and/or as shielding or isolationcomponents or elements. In embodiments, for example, one or more metallayers are used to isolate or shield components (e.g., charge store orcharge store devices) of underlying circuitry or other components of theIC. FIGS. 37 and 38 show an embodiment in which a conductive material ispositioned between the charge store of the respective pixel region suchthat the respective charge store is isolated from the light incident onthe optically sensitive layer. At least a portion of the conductivematerial is in electrical communication with the optically sensitivelayer of the respective pixel region. The metal regions or layers shownand described in FIGS. 37 and 38 can be used as electrical contacts, asdescribed herein, in addition to their function as isolation elements.

FIG. 37 shows the vertical profile of a metal-covered-pixel. The pixelincludes a silicon portion 140, a poly silicon layer 130, and metallayers 120 and 110. In this embodiment 120 and 110 are staggered tocompletely cover the silicon portion of the pixel. Some of the incidentlight 100 is reflected by 110. The rest of incident light 100 isreflected by metal layer 120. As a result no light can reach silicon140. This complete improves the insensitivity to incident light ofstorage node (141).

FIG. 38 shows a layout (top view) of a metal-covered-pixel. In thisembodiment three metal layers (e.g., metal 4/5/6 corresponding to layers108, 110, and 112 in FIG. 9) are used to completely cover the siliconportion of a pixel. Region 200 is metal 4, region 210 is metal 5, andregion 220 is metal 6. Regions 200/210/220 cover approximately theentire pixel area, and thus prevent any light from reaching the siliconportion of the pixel below.

Chip 2000 (Including 2002, 2004, 2008, and 2010)

The above described pixel regions and pixel circuits may be formed on anintegrated circuit and connected through metal interconnect layers asdescribed above. In the example embodiment of FIG. 1, the QDPC 100 mayhave quantum dot pixels 1800 structured on top of an underlyingsubstrate with structures 2002, functional components 2004, andprocessing 2008 capabilities. This underlying substrate, and itsfunctional capabilities, may be referred to as a chip 2000 orsemiconductor chip 2000. Together with the quantum dot pixels 1800above, the chip may provide a plurality of functions such as high-speedreadout, signal multiplexing, decoding, addressing, amplification,analog-to-digital conversion, image sensor processing (ISP), and thelike. The functional components 2004 and processing 2008 capabilitiesmay interface with the pixel circuitry 1700 and with the integratedsystem 2200. In embodiments, the chip 2000 may represent an integratedphotodetector processing element within the QDPC 100 that provideshigh-speed low noise readout, small die area, ability to use largerprocess geometries, combined analog and digital circuitry, higher levelsof integration, image processing, low power, single voltage supply, andnon-planar chips 2000.

The underlying structure 2002 of the chip 2000 may include layers ofintegrated electronics and electrical interconnects 2010, where theintegrated electronics provide the functional components 2004 of theunderlying chip, and the electrical interconnections 2010 provide theinterconnections between these functional components 2004, the pixelcircuitry 1700, and interface connections to off-chip components. FIG. 8shows an example of row and column interconnections between an array ofquantum dot pixels 1800, where row and column interconnects lie indifferent layers within the underlying structure 2002. In embodiments,these row and column traces may be in the upper layers of the underlyingchip semiconductor, and functional components 2004 may be in the lowerlayers. The ability for the additional structures 2002 beneath the pixelarray may provide on-chip processing capabilities that enable innovateproduct solutions.

In embodiments, the underlying structure 2002 of the chip, along withthe pixel structures 1500 and photodetector structures 1400 above, maybe manufactured as a monolithic integrated circuit, also known as an IC,microchip, microcircuit, silicon chip, chip, or the like. The integratedcircuit may have been manufactured in the surface of a thin substrate ofsemiconductor material. In embodiments, the quantum dot structures 1100may be applied on top of this integrated circuit portion to produce theQDPC 100. In this manner, the QDPC 100 maintains the design flexibilityinherent in the tunable, stackable quantum dot structures 1100, withindustry standard processes available to integrated circuittechnologies. The combination of quantum dot structures 1100 andintegrated circuit structures may enable the QDPC 100 to become a lowcost, single element image detection system, fully integrated on asingle chip 2000. In embodiments, the QDPC 100 may also be a hybridintegrated circuit, constructed of individual semiconductor devices, aswell as passive components, integrated onto a substrate or circuitboard. In embodiments, the photodetector structures may be applied toany other underlying structure or technology known to the art.

In embodiments, a hybrid integrated circuit of the QDPC 100 may utilizecommercially available fabrication techniques. FIG. 8 shows an opticalmicrograph of a radiation 1000 sensitive layer formed on a commerciallyavailable electronic read-out integrated circuit (ROIC) chip. In manyembodiments, the radiation 1000 sensitive layer includes a plurality ofQDs, as described in greater detail below. The radiation 1000 sensitivelayer, e.g., the QD layer, overlays and conforms to the features of theunderlying chip. As can be seen in FIG. 8, the electronic read-out chip,e.g., a CCD or CMOS integrated circuit, includes a two-dimensional arrayof rows 2031 and columns of electrodes 2032. The electronic readout chipalso includes a two-dimensional array of square electrode pads 2030which together with the overlying QD layer and other circuitry form atwo-dimensional array of pixels. The row electrodes 2031 and columnelectrodes 2032 allow each pixel (including square electrode pad 2030and overlying QD layer) to be electronically read-out by a read-outcircuit (not shown) that is in electrical communication with theelectrodes. The resulting sequence of information from the ROIC at theread-out circuit corresponds to an image, e.g., the intensity ofradiation 1000 on the different regions of the chip during an exposureperiod, e.g., a frame. The local optical intensity on the chip isrelated to a current flow and/or voltage bias read or measured by theread-out circuit.

In embodiments, a highly integrated image detection system, such as aQDPC 100 consisting of a lower integrated circuit of processingfunctional components 2004 and pixel circuitry 1700, and upper quantumdot structure 1100 consisting of stacked quantum dot pixels 1800, mayrequire testing at the chip 2000 level that more comprehensive than atypical detector. Testing of the QDPD 100, because of its highlyintegrated and multifunctional nature, may be more akin to a combinationof testing for an application specific integrated circuit (ASIC) andoptical testing for a photodetector. In addition, because stacked, orlayered, quantum dot structures 1100 may include what is in essence,multiple integrated detector layers, optical testing may be need to beperformed in stages during the fabrication process in order to fullycharacterize interacting parameters, such as cross-talk throughinsulating dielectric layers between multiple quantum dot materials 200.In embodiments, the testing of the QDPC 100 may require uniquetechniques in order to ensure quality and reliability.

In embodiments, functional components 2004 such as multiplexers anddecoders may provide the on-chip 2000 capabilities to transfer the datafrom the quantum dot pixel 1800 out the edge of the chip 2000, providingthe addressing of the array. Analog circuitry at the end of the columnmay include amplifiers, providing gain and corrections, or analogmultiplexing within the column circuit. Columns may be combined, wherecolumn signals are serially multiplexed. In embodimentsanalog-to-digital conversion may be provided in order to convert thesignals to the digital domain, where other processing components 2008may perform data manipulation, and provides an interface between theimage array and image processing.

In embodiments, the functional components 2004 may include image sensorprocessing (ISP), providing facility for image scanning. For instance,image scanning may allow the examination of a first exposure at lowresolution, determine how to use it, perform a rapid second scan, andprocess on the difference. The luminance signal may have high bandwidthinformation and chrominance has low bandwidth information. In anotherinstance, a first exposure may be at low frequency, then a second athigh resolution, such as red-to-red comparison running across the screenas a normalization on the derivative signal, similar to JPEGcompression. The low frequency could be run as the high-resolution imageis being taken, taking the sensitivity to low radiation 1000 from thebig pixels and spatial information from the small pixels. The bestinformation may be taken from the high frequency and the low frequencyin order to produce the best possible image, such as to leverage for thesake of speed, simplify and implement algorithm to compress the data,collect less analog data, or the like. Individual pixels may come off asdeviation from a background value, where the background value comesquickly with a rough scan. In embodiments, ISP may provide innovativesolutions that may be performed directly on the chip.

In embodiments, processing techniques may be implemented, such as forspatial differentiation, which could result in a power advantage as wellas an improved signal-to-noise advantage. Spatial differentiation mayuse motion to some advantage, as in the way the human eye utilizesmotion in processing the scene. This technique could help compensate forthe inherent shaking of a cell phone or a camera, and may help eliminatepattern noise, because pattern noise may not differentiate. Processingmay also be performed across the entire array, with a delta-alarm thattriggers an increase in sharpness. Processing for edge detection forauto-focus may also be facilitated, with regions determining localsharpness. A direct signal may be fed into a feedback loop to optimizethe degree of sharpness. The use of on-chip processing may providelocalized processing, allowing for a reduction in power and overall sizeof a product.

In embodiments, processing my include binning of pixels in order toreduce random noise associated with inherent properties of the quantumdot structure 1100 or with readout processes. Binning may involve thecombining of pixels 1800, such as creating 2×2, 3×3, 5×5, or the likesuperpixels. There may be a reduction of noise associated with combiningpixels 1800, or binning, because the random noise increases by thesquare root as area increases linearly, thus decreasing the noise orincreasing the effective sensitivity. With the QDPC's 100 potential forvery small pixels, binning may be utilized without the need to sacrificespatial resolution, that is, the pixels may be so small to begin withthat combining pixels doesn't decrease the required spatial resolutionof the system. Binning may also be effective in increasing the speedwith which the detector can be run, thus improving some feature of thesystem, such as focus or exposure.

In embodiments the chip may have functional components that enablehigh-speed readout capabilities, which may facilitate the readout oflarge arrays, such as 5 Mpixels, 6 Mpixels, 8 Mpixels, or the like.Faster readout capabilities may require more complex, largertransistor-count circuitry under the pixel 1800 array, increased numberof layers, increased number of electrical interconnects, widerinterconnection traces, and the like.

In embodiments, it may be desirable to scale down the image sensor sizein order to lower total chip cost, which may be proportional to chiparea. However, shrinking chip size may mean, for a given number ofpixels, smaller pixels. In existing approaches, since radiation 1000must propagate through the interconnect layer onto the monolithicallyintegrated silicon photodiode lying beneath, there is a fill-factorcompromise, whereby part of the underlying silicon area is obscured byinterconnect; and, similarly, part of the silicon area is consumed bytransistors used in read-out. One workaround is micro-lenses, which addcost and lead to a dependence in photodiode illumination on positionwithin the chip (center vs. edges); another workaround is to go tosmaller process geometries, which is costly and particularly challengingwithin the image sensor process with its custom implants.

In embodiments, the technology discussed herein may provide a way aroundthese compromises. Pixel size, and thus chip size, may be scaled downwithout decreasing fill factor. Larger process geometries may be usedbecause transistor size, and interconnect line-width, may not obscurepixels since the photodetectors are on the top surface, residing abovethe interconnect. In the technology proposed herein, large geometriessuch as 0.13 um and 0.18 um may be employed without obscuring pixels.Similarly, small geometries such as 90 nm and below may also beemployed, and these may be standard, rather thanimage-sensor-customized, processes, leading to lower cost. The use ofsmall geometries may be more compatible with high-speed digital signalprocessing on the same chip. This may lead to faster, cheaper, and/orhigher-quality image sensor processing on chip. Also, the use of moreadvanced geometries for digital signal processing may contribute tolower power consumption for a given degree of image sensor processingfunctionality.

An example integrated circuit system that can be used in combinationwith the above photodetectors, pixel regions and pixel circuits will nowbe described in connection with FIG. 70. FIG. 70 is a block diagram ofan image sensor integrated circuit (also referred to as an image sensorchip). The chip includes:

a pixel array (100) in which incident light is converted into electronicsignals, and in which electronic signals are integrated into chargestores whose contents and voltage levels are related to the integratedlight incident over the frame period;

row and column circuits (110 & 120) which are used to reset each pixel,and read the signal related to the contents of each charge store, inorder to convey the information related to the integrated light overeach pixel over the frame period to the outer periphery of the chip

analog circuits (130, 140, 150, 160, 230). The pixel electrical signalfrom the column circuits is fed into the analog-to-digital convert (160)where it is converted into a digital number representing the light levelat each pixel. The pixel array and ADC are supported by analog circuitsthat provide bias and reference levels (130, 140, & 150).

digital circuits (170, 180, 190, 200). The Image Enhancement circuitry(170) provides image enhancement functions to the data output from ADCto improve the signal to noise ratio. Line buffer (180) temporarilystores several lines of the pixel values to facilitate digital imageprocessing and IO functionality. (190) is a bank of registers thatprescribe the global operation of the system and/or the frame format.Block 200 controls the operation of the chip.

IO circuits (210 & 220) support both parallel input/output and serialinput/output. (210) is a parallel IO interface that outputs every bit ofa pixel value simultaneously. (220) is a serial IO interface where everybit of a pixel value is output sequentially.

a phase-locked loop (230) provides a clock to the whole chip.

The input/output pins are described as follows:

VDD is the power supply from which biases on various transistors andother elements are obtained

GND is ground, used in concert with voltage biases to provide potentialdifferences across circuit elements

VFILM is the quantum film bias voltage used to provide a potentialdifference across the optically sensitive layer

VREF is the bandgap reference voltage, used to provide a referencevoltage level for other analog circuits on chip. This reference level istemperature-, voltage-, and process-insensitive.

SDA is a serial control data, used to send in the input data for serialcontrol port. Serial control port can write directly to the on-chipregisters, or perform some simple tasks such as resetting the digitalcircuits.

SCL is a serial control clock. This is the input clock for serialcontrol port.

DOUT<1:N>—parallel output port, N channels. Here N is typically largerthan 8. Every channel is single ended with full digital voltage swing.It is used to output the pixel data with a wide bus at relatively slowspeed.

CLK+/−—serial IO clock, fully differential. This is the clock lane forthe high speed serial output port.

DATA+/−<1:n>—serial output port, n lanes. Here n is typically less than4. Each lane is fully differential with low voltage swing. Pixel dataare sequentially sent out through the lanes.

EXTCLK external clock, used to provide a clock input to the on-chip PLLto generate internal clock for the whole chip.

In example embodiments, the pixel array (100) is implemented by coatingat least one optically-sensitive nanocrystalline layer atop the read-outintegrated circuit array. The layer is extremely sensitive to light, inpart by virtue of its provision of photoconductive gain, wherein forevery photon striking a pixel, a plurality of electrons can be collectedinto the read-out circuit that resides beneath the optically sensitivelayer. The photoconductive layer may be a nonrectifying device, thus itmay provide substantially the same magnitude of current forsame-magnitude biases of opposite polarity.

In an example embodiment, the electrodes providing voltage bias may belaterally opposed to one another, that is to say they may reside withinthe same plane. In this case the predominant direction of current flowwithin the photosensitive layer is in the lateral direction. Theelectrodes may be configured in a pattern such that, even if theoptically sensitive layer is continuous across the entire array, thecurrent that is collected within each pixel electrode is relatedpredominantly to the illumination intensity striking that pixel regiononly. Electrode configurations that accomplish this substantialisolation between pixels include those of a closed geometry, wherein agrid (such as one that repeats an array of squares, triangles, hexagons,or other closed shapes) provides a first bias, and electrodes residingat the centre of each grid repeat unit provide a second bias, and theseelectrodes providing a second bias collect the current flowingsubstantially within each closed grid repeat unit. The electrodesbiasing the device need not be transparent but may be opticallyreflective and absorptive in some embodiments. These configurations areexamples only and other configurations may be used in other embodiments,including vertically stacked electrodes, transparent electrodes andother electrode and photoconductor configurations described herein. Forexample, the electrodes may, in an alternative embodiment, be verticallyopposed to one another, such that the flow of photocurrent issubstantially in the vertical direction.

In a particular example embodiment, when 0.11 um CMOS technology node isemployed, the periodic repeat distance of pixels along the row-axis andalong the column-axis may be 900 nm, 1.1 um, 1.2 um, 1.4 um, 1.75 um,2.2 um, or larger. The implementation of the smallest of these pixelssizes, especially 900 nm, 1.1 um, and 1.2 um, may require transistorsharing among pairs or larger group of adjacent pixels.

Very small pixels can be implemented in part because all of the siliconcircuit area associated with each pixel can be used for read-outelectronics since the optical sensing function is achieved separately,in another vertical level, by the optically-sensitive layer that residesabove the interconnect layer.

Because the optically sensitive layer and the read-out circuit thatreads a particular region of optically sensitive material exist onseparate planes in the integrated circuit, the shape (viewed from thetop) of (1) the pixel read-out circuit and (2) the optically sensitiveregion that is read by (1); can be generally different. For example itmay be desired to define an optically sensitive region corresponding toa pixel as a square; whereas the corresponding read-out circuit may bemost efficiently configured as a rectangle.

Since gain may be provided by the optically sensitive layer, such that(for example) each photon incident on an optically-sensitive region mayresult in the collection of (for example) 10 electrons, a highlysensitive image sensor may be realized even using simplified pixelread-out circuits that employ a small number of transistors. Even usinga circuit employing only three transistors (of which at least one may beshared with other pixels), high sensitive to light may be obtained.

For example, in a conventional pixel based on a photodiode having anoverall quantum efficiency of 50%, and on which an intensity of 1 nW/cm2is incident, then in a 1/15 second integration period, a 1.1 um×1.1 umpixel would supply an average of 1 electron's worth of photocurrent tobe read by the read-out circuit. If the overall circuit read noise were3 electrons, then this level of intensity would essentially beundetectable by this pixel and its read-out circuit.

In contrast, in the case of a pixel having the same area and integrationtime, but having 90% quantum efficiency and a gain of 5, an average of10 electrons' worth of photocurrent would be available to be read by theread-out circuit. If this overall circuit read noise were 3 electrons,then this level of intensity would be detectable by this pixel and itsread-out circuit. What is more, even if a simpler and/or smaller circuitwere built that provided a worse read-out noise equivalent to 6electrons, this low level of intensity would still be detectable by thispixel and its read-out circuit.

In an imaging array based on a top optically sensitive layer connectedthrough vias to the read-out circuit beneath, there exists no imperativefor the various layers of metal, vias, and interconnect dielectric to besubstantially or even partially optically transparent, although they maybe transparent in some embodiments. This contrasts with the case offront-side-illuminated CMOS image sensors in which a substantiallytransparent optical path must exist traversing the interconnect stack.In the case of conventional CMOS image sensors, this presents anadditional constraint in the routing of interconnect. This often reducesthe extent to which a transistor, or transistors, can practically beshared. For example, 4:1 sharing is often employed, but higher sharingratios are not. In contrast, a read-out circuit designed for use with atop-surface optically-sensitive layer can employ 8:1 and 16:1 sharing.

The photoconductive layer may possess a bias-dependent gain, such thatat higher bias, the gain is higher, and that at lower bias, the gain islower. Read-out circuits associated with each optically sensitive regionintegrate, store, and participate in relaying to the chip's periphery anelectrical signal related to the light intensity that struck the pixelprimarily during the electronic integration period. The read-outcircuits may be configured such that the bias across the opticallysensitive layer decreases throughout the integration period, resultingin a decrease in gain throughout the integration period. The decrease ingain throughout the integration may be more pronounced when a largercurrent is flowing, i.e. when more light is striking the pixel. Thus theeffective gain may be lower when the optically sensitive region beingread is more strongly illuminated. As a consequence, for a given rangeof voltage (such as a span of 1 V) on an electrical node that provides asignal related to the integrated light intensity, corresponding forexample to the input range of an analog-to-digital converter, a greaterrange of light intensities may be represented. For example, an 80 dBrange or greater range in light intensities may be represented over a 1V swing.

Spectral information may be obtained from the pixel array by forming apatterned color filter array above the optically sensitive layer:different color filters ensure that different spectral bands of lightare incident on the photoconductive pixels beneath.

In an alternative embodiment, color-selective stacked pixels may beformed in which a plurality of optically-sensitive layers aresuperimposed in the vertical direction. The upper layer or layers areselected to have a larger bandgap than the lower layers. As aconsequence the upper layer or layers provide sensing ofshorter-wavelength light and block this shorter-wavelength light, suchthat the lower layer or layers primarily sense longer-wavelength light.

Spectral information in any of the embodiments mentioned above mayinclude X-ray, UV, visible (including particular colors within thevisible such as red, green, and blue), near-infrared, andshort-wavelength infrared. It is of interest to produce multicolor,multispectral, or hyperspectral images that provide aligned, or fused,images wherein different pixels (colored or false-colored) presentoverlaid versions portraying the spectral content within distinctspectral bands.

Row/column circuitry (110 & 120) provides for reset of each pixel andreading of the signal related to the contents of each charge store. Thispermits conveyance of the information relating to the integrated lightstriking each pixel over the frame period to the outer periphery of thechip. One means of reading out the array includes use of a number of rowcircuits approximately equal to the number of rows in the pixel array;and a number of column circuits approximately equal to the number ofcolumns in the pixel array. For example a 300×200 pixel array will beread out using 200 rows and 300 columns. The row and column circuits arethen pitch-matched to the pixel array row and column.

In another embodiment known as row/column swap, the row and columncircuits are designed with greater flexibility. To read out a 300×200pixel array, 600 column circuits and 100 row circuits may be employed.Since the row circuits are complex, this may provide an advantage suchas making available a larger area to the design of the row circuits. Ifcolumn circuits are particularly complex, in this example one coulddesign 150 column circuits and 400 row circuits, giving more area to thecolumn circuits.

Column circuitry may incorporate a fixed current sources employed toprovide current to read out each pixel's source-follower. In analternative embodiment, known as flexible column, the column circuit mayinstead incorporate a voltage source or floating node. This enablesfeedback during reset and saves power during readout, resulting in noisereduction and power saving. The flexible column can also be used astesting point to provide known input to the downstream circuits such asADC. This may assist or improve the calibration process. The result maybe less noisy column readout and/or improved uniformity.

The bias block (140) contributes to providing biasing of the opticallysensitive layer. Embodiments may include provision of negative voltageto one node of the optically sensitive layer in order to providesufficient electric field between the two electrodes such that anappropriate level of photoconductive gain may be provided. Embodimentsmay include provision of a variety of possible voltages to the opticallysensitive layer in order to select the level of gain provided by theoptically sensitive layer. The bias block (140) may therefore includeboth negative voltage, including more-negative values than −1 V (e.g.−1.5 V, −1.7 V, −2 V), and also provision of programmable voltages.

The provision of gain within the optically sensitive layer also hasimplications on the design of the A/D block (160). Normally, gain isrequired in front of the analog-to-digital converter in order topreserve signal-to-noise across the signal chain. Gain inherent in theoptically-sensitive layer lessens the requirement for high gain in frontof the analog-to-digital converter.

Analog-to-digital converters in conventional image sensors often employconstant differences (measured in mV) between the levels that representunity-increasing digital-number values output by the analog-to-digitalconverter. This arises from the fact that conventional image sensorsemploy constant-quantum-efficient photodetectors, so that differences inlight levels incident on a photodetector translate linearly intodifferences in currents produced by photodiodes, and thus result inlinearly proportional differences in the voltage on the node to be readby a column circuit. However, optically sensitive layers having gain mayproduce a photocurrent which depends in a nonlinear dependence ofphotocurrent on intensity. For example, for a given bias,I=a*L−b*L^2

where I is the photocurrent is L is the intensity of light incident onthe pixel. This is an example of a simple polynomial relationshipapproximating the photocurrent.

In this case, the light level may be inferred from knowledge of themeasured current and the coefficients a and b and by inverting the knownapproximately polynomial relationship.

The inversion of the relationship may be accomplished in one of a numberof ways, including in combination:

An analog circuit may be employed prior to the conveyance of the signalinto the analog-to-digital converter that inverts or partially invertsthe functional relationship between I and L.

The relationship between analog levels input to the analog-to-digitalconverter, and digital numbers output from the analog-to-digitalconverter, may be rendered nonlinear in such a manner as to invert thefunctional relationship between I and L.

A digital circuit and algorithm may be deployed, either on an imagesensor system-on-chip or on a separate chip, to implement inversion ofthe functional relationship between I and L mathematically in thedigital domain.

Block (170) (image enhancement) represents one on-chip location in whichlinearization of the nonlinear response of the film may be implementedin the digital domain.

Also in Block (170) may be implemented the adjustment of reported pixelchannels which are offset or linearly scaled or both as a consequence ofthe layout of the underlying read-out circuit. For example, read-outcircuits may be designed such that adjacent (e.g. odd-and even-numbered)columns employ at least one transistor whose implant profile is mirroredrelative to the adjacent column. As another example, read-out circuitsmay share transistors. In each case, slight offsets in alignment betweenCMOS circuit layers (such as an implant layer and a metal layer) mayresults in slight differences in dark current, gain, or both, thatrepeat periodically across the array. The image enhancement block (170)may be used to correct these offsets and invert these scaling factors.

Quantum Confinement

An embodiment of the photodetector 1400 exhibits the simultaneousattainment of sensitivity, gain, tenability, and wide dynamic range in avisible-wavelength-sensitive spin-cast photodetector 1400. Anoptimally-processed photodetector 1400 may provide D* of 10¹³ Jonesacross the entire visible spectrum, compared with silicon photodiodes'˜2 10¹² Jones at 970 nm and even lower in the visible. Photoconductivegains may lie between 1 and 100, and configurations of the photodetector1400 can exhibit photoconductive gains exceeding 100 A/W.

Bulk PbS may have a bandgap of approximately 0.4 eV, and the quantum dotmaterials described herein increase dramatically the degree of quantumconfinement in the quantum dot materials 200 to make the visible-onlycolloidal quantum dot photoconductive detector 1400 described herein.The synthetic procedures of an embodiment enable the synthesis ofquantum dots 1200 with absorption onset below 800 nm, as describedherein. FIG. 3 i(a) shows the absorption spectrum of the resultantquantum dots, under an embodiment. FIG. 3 i(b) shows that thenanoparticles can have diameters of 3 nm and exhibit faceting, under anembodiment. As synthesized, the nanocrystals of an embodiment can bestabilized with oleic acid, a configuration expected and observed toimpede carrier transport due to the oleate ligand's long insulatingchain. Exchanging to shorter ligands such as butylamine may result in adramatic increase in conductivity. Whereas in the case of larger 4-6 nmnanoparticles, monodispersity and excitonic features are preserved afterligand exchange in solution phase, in the small nanocrystal case, theprocedure may lead, instead, to the formation of nanostrings (see, forexample, FIG. 3 i(c) and the related description elsewhere herein) aspreviously seen for PbSe nanoparticles (Cho, K. S. Talapin, D. V.Gaschler, W. Murray, C. B. Designing PbSe Nanowires and Nanoringsthrough Oriented Attachment of Nanoparticles Journal of the AmericanChemical Society 127, 7140-7147 (2005)); and, a loss of an abruptabsorption onset resulting from irreversible aggregation (see, forexample, FIG. 3 i(a) (dashed curve) and the related description herein).

An approach that preserves a sharp, short-wavelength absorption onset isdescribed below. Ligand exchange in the solid state, once thin films areformed, may limit the number of nanocrystal reattachment sites anddramatically improve conductivity without dramatically alteringquantum-confined energy levels. PbS nanocrystals dispersed in toluenecan be spincoated onto glass substrates with gold interdigitatedelectrodes with a 5 μm spacing (shown in FIG. 3 l) to form a solid statefilm with thickness of 360 nm. The film is then treated in a mixture of20% butylamine in acetonitrile over approximately two days. Followingthis solid-phase ligand exchange, the film may exhibit conductivity withdark current density 600 μA cm⁻² at applied field of 20 V μm⁻¹ (shown inFIG. 3 n). Untreated samples or samples treated with acetonitrile alonemay not exhibit measurable conductivity.

The photodetectors 1400 of an embodiment can be characterized for darkcurrent, responsivity, and noise current as described in detail herein.FIG. 3 j shows the optoelectronic performance of the photodetectors ofan embodiment. FIG. 3 j(a) exhibits spectral responsivity and normalizeddetectivity. The photoconductive gain may reach a maximum at wavelength400 nm of ˜113 A W⁻¹ at 15 Hz. In contrast, conventional siliconphotodetectors exhibit a maximum responsivity at ˜970 nm which may dropin the visible spectral range. The quantum dot photodetector 1400 of anembodiment exhibits an increasing responsivity at shorter wavelengthsand optimal response in the visible spectrum. With respect tosensitivity, FIG. 3 j(a) shows a direct comparison between a typicalsilicon photodetector (as in Electro Optics Technology, biased silicondetector model ET-2000) of area similar to the solution-processedthin-film photodetector 1400 of this embodiment. Across the entirevisible spectra range, the quantum dot photodetector 1400 exhibits atleast an order of magnitude better noise-equivalent power (NEP) than itscrystalline silicon counterpart.

The measured noise current spectrum for the photodetector 1400 of theembodiment is shown in the inset of FIG. 3 j(b). At low frequenciesnoise current density follows closely the responsivity curve, suggestingthat the carrier traps responsible for high-gain may also contribute tonoise, while at higher frequencies, white noise may dominate. TheJohnson noise of the detector may be estimated by (4kTB/R)^(1/2) to be˜0.9 fA Hz^(−1/2) whereas the shot noise limit (2qI_(d)B)^(1/2) is found0.04 pA Hz^(−1/2) where k is Boltzman's constant, T the temperature, Rthe resistance of the detector in dark, B the noise bandwidth, q theelectron charge and I_(d) the dark current. The photodetector 1400 ofthe embodiment may approach the shot noise limit to within 3-dB at 80Hz.

The quantum dot photodetector 1400 of an embodiment exhibits greatersensitivity when compared to silicon beyond 50 Hz, as shown in FIG. 3j(c), where D* is plotted as function of frequency (the inset also showsthe NEP versus the modulation frequency). At low frequencies (<5 Hz) thedetector may exhibit D*˜10¹³ Jones.

The trap states of the quantum dot photodetector of an embodimentresponsible for photoconductive gain are characterized, for example,with reference to FIG. 3 k(a). FIG. 3 k (a) shows the measuredresponsivity as a function of modulation frequency for a number ofdifferent optical power levels incident on the device is shown. Theresponsivity of the detector may decrease as the optical power may beincreased. This may be attributed to filling of the lowest-lying,longest-lived trap states that provide the highest photoconductive gainat low intensities. This may be confirmed by the fact that, at highintensities, the 3 dB bandwidth may extend to higher electricalfrequencies.

In order to characterize the impact of high-gain trap state filling onthe dynamic range of the solution processed detector, the dependence ofphotocurrent on optical intensity at a modulation frequency of 30 Hz ismeasured. A monotonic, though at high intensities sublinear, dependenceof photocurrent on intensity over more than 7.5 orders of magnitude inincident intensity corresponding to over 75 dB of intensity dynamicrange may be observed (FIG. 3 k(b)). The inset of FIG. 3 k(b) shows theonset of responsivity decrease due to the filling of the high gain trapstates at higher intensities that may be responsible for gaincompression.

The teachings herein relating to the photodetector 1400 of theembodiment illustrate improvements in one or more of sensitivity,dynamic range, and gain when compared to typical crystalline siliconphotodiodes. While the materials and processes of an embodiment are usedto generate or produce quantum dot photodetectors, quantum dot pixels ordevices can be produced that incorporate or integrate the quantum dotphotodetectors.

A multi-color device (e.g., two-color, etc.) or pixel, also referred toherein as a quantum dot pixel, is produced under the teachings herein bystacking a small-quantum-dot 1200, larger-bandgap photodetector 1400atop a large-dot, small-bandgap (exciton peak at 1230 nm) device asillustrated in the inset of FIG. 3 l, and as described in detail belowin the description on geometric layouts. FIG. 14 j also shows themeasured spectral responsivity of each detector in the stack, under anembodiment. The spectral responsivity of the small-bandgap detectorprior to stacking is also shown to demonstrate the achieved suppressionof responsivity in the visible by over 10-dB at 400 nm. Thus, the valueof quantum size-effect tenability inherent to colloidal quantum dots1200 under an embodiment is depicted in FIG. 3 l.

Photodetector Geometric Layouts 1402

The quantum dot pixels 1800 described herein can be arranged in a widevariety of pixel layouts 1600. Referring to FIGS. 5 a-p for example, aconventional pixel layout 1600, such as the Bayer filter layout 1602,includes groupings of pixels disposed in a plane, which different pixelsare sensitive to radiation 1000 of different colors. In conventionalimage sensors, such as those used in most consumer digital cameras,pixels are rendered sensitive to different colors of radiation 1000 bythe use of color filters that are disposed on top of an underlyingphotodetector, so that the photodetector generates a signal in responseto radiation 1000 of a particular range of frequencies, or color. Inthis configuration, mosaic of different color pixels is referred tooften as a color filter array, or color filter mosaic. Althoughdifferent patterns can be used, the most typical pattern is the Bayerfilter pattern 1602 shown in FIG. 5 a, where two green pixels, one redpixel and one blue pixel are used, with the green pixels (often referredto as the luminance-sensitive elements) positioned on one diagonal of asquare and the red and blue pixels (often referred to as thechrominance-sensitive elements) are positioned on the other diagonal.The use of a second green pixel is used to mimic the human eye'ssensitivity to green light. Since the raw output of a sensor array inthe Bayer pattern consists of a pattern of signals, each of whichcorresponds to only one color of light, demosaicing algorithms are usedto interpolate red, green and blue values for each point. Differentalgorithms result in varying quality of the end images. Algorithms maybe applied by computing elements on a camera or by separate imageprocessing systems located outside the camera. Quantum dot pixels may belaid out in a traditional color filter system pattern such as the BayerRGB pattern; however, other patterns may also be used that are bettersuited to transmitting a greater amount of light, such as Cyan, Magenta,Yellow (CMY). Red, Green, Blue (RGB) color filter systems are generallyknown to absorb more light than a CMY system. More advanced systems suchas RGB Cyan or RGB Clear can also be used in conjunction with Quantumdot pixels.

In one embodiment, the quantum dot pixels 1800 described herein areconfigured in a mosaic that imitates the Bayer pattern 1602; however,rather than using a color filter, the quantum dot pixels 1800 can beconfigured to respond to radiation 1000 of a selected color or group ofcolors, without the use of color filters. Thus, a Bayer pattern 1602under an embodiment includes a set of green-sensitive, red-sensitive andblue-sensitive quantum dot pixels 1800. Because, in embodiments, nofilter is used to filter out different colors of radiation 1000, theamount of radiation 1000 seen by each pixel is much higher.

In contrast to conventional pixels, quantum dot pixels 1800 may berendered sensitive to varying wavelengths of radiation 1000. Referringto FIGS. 5 b through 5 f, quantum dot pixels 1800 may be made sensitiveto one color of radiation 1000, such as the blue pixel of FIG. 5 b andthe red pixel of FIG. 5 c. Such pixels may be used in a wide range oflayouts, such as the Bayer pattern 1602 of FIG. 5 a. As described inthis disclosure and in the documents incorporated by reference herein,quantum dot pixels 1800 may also be made sensitive to more than onecolor of radiation 1000. Referring to FIG. 6 d, a quantum dot pixel mayinclude a set of vertical layers of quantum dot material 200 or a singlelayer of quantum dot material 200 that is differentially sensitive, sothat a single planar location on a chip may be sensitive to multiplecolors of radiation 1000, such as red, green and blue, as depicted inFIG. 5 d or UV, blue, green, red and infrared, as depicted in FIG. 5 e.Thus, a multispectral quantum dot pixel 1604 may be used in variouspixel layouts 1600. Quantum dot materials 200 may be made that aresensitive to a wide range of colors within the color gamut, includingspecific colors or groups of colors. While a standard RGB pixel hasadvantages in its ability to be used with conventional circuit designs,improved sensors and displays may be provided with more colors in thegamut. To use such colors, it is advantageous in embodiments to stacklayers of quantum dot material 200 vertically in order to createmulti-spectral pixels that are sensitive to more colors of radiation1000. Being able to capture a larger part of the spectrum of radiation1000, both visible and non-visible to the human eye, will allow for amuch higher information density per given pixel, which in turn allowsfor a much higher resolution sensor within a given footprint. Forexample, a ¼ inch optical format device with 1 million pixels thatcapture either R or G or B with each pixel is typically viewed as havinga resolution of a “megapixel”. A ¼ inch optical format sensor with 1million pixels, each pixel capable of capturing R and G and B, wouldthus have triple the resolution. This may be a critical differentiatorin imaging systems where cost and size are critical.

Referring to FIG. 5 f, a multispectral pixel element 1604 may also becreated by locating quantum dot materials 200 at different positions ona plane, in various configurations and patterns.

Referring to FIG. 5 g, pixels 1800 of different sizes may be used in agiven pixel array 1600. For example, a large green element may besurrounded by smaller red and blue elements. Any range and combinationof colors may be used in such configurations.

Referring to FIG. 5 h, multi-spectral pixels 1604 may be arranged invarious patterns different from a Bayer pattern 1602, such as a simplerectangular arrangement where each position in the array is filled witha multi-spectral pixel 1604. The full image information may be storeddirectly with the pixel, such as with a memory element located proximalto or on the pixel, so that compression algorithms, such as, oranalogous to, JPEG and TIFF algorithms, can be applied without (or withminimal) separate processing.

Referring to FIG. 5 i, multi-spectral pixels 1604 may includefull-spectrum, multi-spectral quantum dot pixels 1608, such as withsensitivity to IR and UV information, in addition to color information.Thus, any of the arrays described herein may include one or morefull-spectrum, multi-spectral quantum dot pixels 1608.

Referring to FIG. 5 j, a quantum dot pixel layout 1600 may also includepixels of different sensitivities, such as those sensitive to singlewavelengths of radiation 1000 (such as green, those sensitive to acollection of visible colors (such as red, green and blue), thosesensitive to IR and those sensitive to UV. Thus, a pixel array 1600 maybe a mix of multi-spectral pixels 1604, single-spectrum pixels, andspecialized pixels such as those sensitive to non-visible wavelengths.In addition, pixel arrays may include planar pixels as well as pixelswith vertical elements, such as vertical, multi-spectral pixels 1604.FIG. 5 k and FIG. 5 l show other arrangements of quantum dot pixels1800, including various mixes of pixels of different spectralsensitivities.

Referring to FIG. 5 k, pixel layouts 1600 may be constructed of pixelsof different planar shapes, including the rectangular pixels of theBayer pattern 1602, but also other shapes such as hexagons (as depictedin FIG. 5 m) or triangles (as depicted in FIG. 5 n). There is benefit toapproximate the point-spread function of a given lens system, whichwould typically image a point source of radiation 1000 more in acircular pattern than a square pattern, thus being able to approximatecircular patterns (e.g. through the use of a hexagonal shape), fulleruse of the resolving capability of a lens system may be attained. Pixellayouts 1600 may also be provided with offset rows and columns, ratherthan strictly rectangular layouts 1600. It should be noted that in orderto maximize fill factor (the percentage of planar array covered by imagesensors, as compared to dark space or other elements), shapes that filla plane may be preferred, such as squares, rectangles, hexagons andtriangles. However, with the high sensitivity made possible in variousembodiments disclosed herein, it may also be preferable to adopt othergeometries, as adequate performance may be obtained without filling anentire plane, particularly in pixel layouts 1600 that have verticaldimensions. Thus, space in a pixel layout 1600 might be reserved forother components, such as components used for dark references,components used to generate power (such as through photovoltaiceffects), and other components.

Referring to FIG. 5 o, a quantum dot pixel 1800, such as amulti-spectral quantum dot pixel 1604 or other pixel, may be provided inassociation with an optical element 1610, such as a prism, filter, lens,microlens or the like. Thus, pixel arrays 1600 may be created thatinclude elements that use approaches used in filter-based or lens-basedapproaches, such as used in conventional image sensors, CCD arrays, orthe like. In such embodiments, a pixel 1800, such as a multi-spectralpixel 1604, can be thought of as a spectrometer, with an optical elementconfigured to distribute radiation 1000 to sub-pixels below. Since thepixels 1800 disclosed herein can be produced with a very large chief rayangle, it may be possible to provide an optical element, such as agrating spectrometer, that separates spectral components. Such a gratingmay be created by placing a high refractive index polymer over the pixel1800, masking a portion of the polymer, and removing the unmaskedportion to leave a grating. Other techniques may be used to produce adispersive element, such as putting a diffraction grating below aquantum dot material layer 200, allowing radiation 1000 to pass throughand bouncing a portion of the radiation 1000 to detectors underneath thelayer. In various embodiments a grating spectrometer could separatedifferent color components of radiation 1000 with absorbing theradiation 1000; therefore, it would allow differential color sensitivitywithout losing power in the incoming radiation 1000. Thus, this approachwould allow color sensitivity in low radiation 1000 situations wherefilters remove too much of the signal.

Pixel layouts 1600 such as those described herein may be configured toachieve color images with very small pixels relative to those used inconventional image sensors. Traditional methods start to reach a limitat 1.2 microns in pixel size, while the pixels 1800 described herein canbe provided at much smaller sizes and can provide much better colorfidelity even at large sizes. Thus, the pixels 1800 and pixel layouts1600 described herein allow for high image quality on small, inexpensivechips that have large numbers of pixels. Among other things, the layouts1600 described herein also allow an increase in the angle at which theimage sensors can receive and thus sensitively detect radiation 1000.This allows making very thin pixels 1800 and very thin camera systemsthat absorb desired wavelengths of radiation 1000 without the negativeeffects that can arise out of optical crosstalk, where one pixelreceives radiation 1000 information that should have been captured by aneighboring pixel.

With reference to FIG. 1, the pixel layouts 1600 of an embodiment can beassociated with suitable pixel circuitry 1700 to allow a pixel to beread with any of a range of conventional pixel readout electronics, suchas the electronics used to read Bayer mosaic pixels, vertically-stackedpixels, CCD arrays, and other image sensor arrays. For example, a pixellayout 1600 may be associated with circuitry 1700 that allows for use ofstandard row-and column-based readout circuitry, which in turn allowsthe quantum dot pixel chip 100 to be used in a wide range of hardwareand devices, without requiring special integration techniques.

The pixel layouts 1600 described herein generally remove any requirementfor a separate, light-absorbing color filter. With continuing referenceto FIG. 1, as rays traverse the layers of a conventional image sensor,stray radiation 1000 can hit the photodetecting element without firstpassing through the filter, producing crosstalk between neighboringsensor elements that have different companion color filters. The pixels1800 disclosed herein can eliminate the need for the filter and reducethe parallax problem. In embodiments, pixel layouts 1600 could beassociated with elements that block stray radiation 1000 that impingesupon neighboring pixels, or image data can be processed in a way thatallows resolution of crosstalk among pixels. Thus, processing of imagedata from the pixel layouts 1600 can be simplified relative togeometries that require resolving spatial differences between a filteror other optical element and the image sensor.

Pixel layouts 1600 disclosed herein include pixels having varioussensitivities to different bands of the electromagnetic spectrum. Inembodiments, color sensitivity is based on absorption onset as radiation1000 penetrates quantum dot materials 200. For example, a layer may besensitive to blue, a deeper layer may be sensitive to blue and green,and a deeper layer may be sensitive to blue, green and red. If the bluelayer is placed on top, it may absorb much of the blue radiation 1000,allowing the blue-green layer to respond primarily to green radiation1000. Similarly, the blue-green sensitive layer may absorb the remainingblue radiation 1000, and the green radiation 1000, leaving primarily redradiation 1000 for the next lower layer. Thus, reading signals from thedifferent layers may result in obtaining relative levels of red, greenand blue radiation 1000. This approach may be generalized to othercolors of radiation 1000, with layers in the appropriate order. Inembodiments, signals from different layers may be manipulated, such asby subtracting, to determine a relative signal from different layers, inorder to infer an intensity of each color.

The various embodiments disclosed herein allow for creating a singlesensor that allows taking images across a wide range of electromagneticradiation 1000. Thus, a single detector can provide multiple functions,such as a color camera in combination with a night vision device, acolor camera combined with an x-ray, or the like. Thus, the pixellayouts 1600 disclosed herein potentially overlay images in differentspectral regimes, allowing, for example, a single camera to use oneradiation 1000 band for imaging during the day and use the same pixelsfor imaging in a second radiation 1000 band. For example, at night, orin low radiation 1000, IR-sensitive components of a pixel layout 1600may be used to produce a black and white image at very high sensitivity.Multi-spectral pixel layouts 1600 may thus be used in multi-spectralproducts such as cameras used to inspect aircraft wings, medical imagesensors (such as for x-rays or cancer detection), image sensors used todetect laser targeting while providing an image of an environment (suchas in military applications), or a wide range of other applications.

Multiple layers of quantum dot structures 1100 may be vertically stacked(i.e. one on top of another) as described herein, wherein the verticalstack creates a multi-spectral pixel. In creating a vertically-stackedmulti-spectral pixel, the upper layers may absorb and simultaneouslydetect certain wavelengths of radiation 1000; transmitting otherwavelengths for subsequent detection in lower layers. It is desirablefor each layer to achieve substantially complete absorption within thespectral region for which it is designed to be responsive. Outside ofthis band, and within the band(s) for which lower-down layers areresponsive for the detection of radiation 1000, this upper-lying pixelshould be substantially transmissive.

In embodiments the pixels of each vertically stacked quantum dot layerare separately electrically connected to their respective pixel circuitelements 1700. The vertically stacked quantum dot structures 1100 may beseparately addressed electrically such that the portion of the radiation1000 received by each layer of the stack is independently read once itis converted to an electrical signal. In embodiments vertically-stackedquantum dot structures 1100 and its associated pixels may be readlaterally. Each active layer may be biased using contact arrays on thesides of each layer, for example. In embodiments, the layers aresubstantially electrically isolated from one another. For example, eachactive layer may be separated in the vertical dimension and there may bea substantially electrically insulating material provided between theactive layers. In another embodiment, the biasing and reading of thevertically-stacked quantum dot structures 1100 involves the use ofvertically-stacked electrodes contacting each photodetector layer. Inthese embodiments, whether the electrical interconnects are laterally orvertically arrayed, the electrodes are connected to vias that conveyelectronic signals down to the read-out circuit layer beneath (e.g.,pixel circuitry 1700.) In embodiments where vertically stacked quantumdot layers are provided, the spectral characteristics of the severallayers needs to be considered in determining which layer is to beprovided on top of another. In embodiments the upper layer issubstantially transparent to the wavelengths of radiation 1000 that areto be received by the layers beneath. While embodiments stack thequantum dot layers in an order that provides at least partialtransmission of radiation 1000 to the lower layers, other embodimentsmay not be so limited.

The formation of the photosensitive layer near the top surface of theimage sensor chip, rather than within the silicon crystal that is usedto implement transistors and other electronics for read-out, carriers anumber of advantages. The top surface can be more nearly filled withphotosensitive material (e.g. near 100% fill factor). The increased fillfactor provides both improved sensitivity at low radiation 1000 levelsand higher signal to noise at all radiation 1000 intensities. The directincidence of radiation 1000 upon the photosensitive layer (e.g. quantumdot structure 1100) can be achieved without requiring opticalmanipulation (such as achieved using microlenses) to convey radiation1000 down into the bottom of a high-aspect-ratio stack of interconnectin dielectrics. The use of this top-surface detector achieves themaximal conveyance of light to the light-sensitive device, providing fora maximum of sensitivity, and also minimizes optical crosstalk. Whilecertain embodiments may use lenses or microlenses, the generalelimination of the requirement for microlenses improves the quality ofthe photodetector. Generally, the use of microlenses in the conventionalphotosensor systems limits the chief ray angle and also requiresshifting of microlenses across the image sensor, rendering the imagesensor design tightly coupled to microoptics design. In embodiments aphotosensor according to the principles described herein havetop-surface detectors that achieve high sensitivity at low radiation1000; top-surface detectors that substantially preserve opticalsignal-to-noise ratios at higher intensities; detectors and read-outsthat together achieve a high dynamic range; and detectors and read-outcircuits that together implement acceptably low image lag such that theappearance of memory effects, or ghosting, in images is avoided.

In embodiments described herein, the use of multi-spectral pixels 1604may allow for the use of pixels in other spectral domains. One suchembodiment may include use of pixels in the pixel layouts 1600 foroptical time-of-flight measurements, such as laser scanning or pixelreadouts that are synchronized with pulsed radiation 1000 sources. Thus,a pixel layout 1600 may include one or more time-of-flight pixels aswell as image sensing pixels. In such embodiment the readoutarchitecture would include elements suitable for reading image sensingpixels as well as elements suitable for reading time-of-flight data usedin laser scanning or other time-of-flight techniques. Sincetime-of-flight approaches do not necessarily require high spatialresolution, a layout may include tightly spaced multi-spectral pixels1604 with loosely spaced time-of-flight pixels.

In embodiments pixels 1800 of various types may be stacked in verticalarchitectures. For example, pixels 1800 configured in a planar layout1600 may be arranged to sense an image within a radiation 1000 band,while a different pixel layout 1600 may be placed above or below theinitial layer, such as to perform other sensing, such as for obtainingtime-of-flight data for 3D spatial resolution.

An aspect of the present embodiment relates to fill factors (i.e. theareas of the photodetection layer that are not consumed with quantumdots 1200). There is typically a fractional area of the surface that isoccupied by metal, or other non-photosensing material, as opposed tophotosensing material. Embodiments minimize the amount of area filled bymetal, as described herein. In embodiments, the metal-covered area isfunctional (e.g. it provides blockage for dark current readings).

In embodiments, the fill area or metal area deliberately obscures someof the photosensing material; the top layer may partially obscure anunderlying structure. This may render some of the material as notradiation-sensitive (i.e. an insensitive reference, rather than a darkreference). An electrode from an electrical interconnection 1404 may beplaced in a dark region under one of the shaded areas to make darkmeasurements.

In embodiments the underlying metallic layer occupies a large fractionof the photodetection area and custom designs of the metal may be usedto create certain advantages. For example, one may want squares, points,or other shape with metal layer.

Aspects that can be altered in a pixel 1800 under the teachings hereininclude pattern, fill factor, sensitivity, shape of pattern, contactdesign, contact materials, infill between the pixels, contacts out ofmulti-layered structures, transparent layers, sharing of components, topcontact pattern and the like. Embodiments may not require a topelectrical contact. The top electrical contact may not need to betransparent; or may be transparent only within a certain spectral bandor within certain spectral bands.

In embodiments, a multiplicity of adjacent or near-adjacent pixels sharetransistors and/or other circuits and/or circuit components amongpixels.

In embodiments, a multiplicity of adjacent or near-adjacent pixels sharedark-reference photoconductors, or references made usinginsensitive-conductors, among pixels.

In embodiments the photodetector geometric layout 1402 includes apatterned top contact. The top contact layer may be a grid, and the gridcan incorporate holes for the penetration of radiation 1000.

Embodiments include those that provide optical resonance structures. Inan optical resonance structure the thickness of a quantum dot structurelayer corresponds to an integer multiple of a quarter-wavelength ofradiation 1000 is deemed of interest. This approach modulates theeffective absorbance of this color of radiation 1000 relative to allothers. For example, this optical resonance approach can achieve anincreased absorbance of some colors of radiation 1000 compared to whatwould be obtained via a single pass of radiation 1000 through thatmaterial.

Embodiments involve setting an electrical interconnection deep or in ashaded area of the quantum dot structure 1100. A contact may be burieddeep enough in the material or under an occlusion (e.g. under a metalpiece, under a non-transparent dielectric, etc.). A dark measurementcould then be made by measuring the charge associated with the ‘darkcontact.’ Another electrical interconnection 1404 may make electricalcontact with and read charge from a more active region of the quantumdot structure 1100 to make the radiation 1000 readings. The radiation1000 readings can then be compared to the dark measurement to create areferenced radiation 1000 reading. In embodiments the quantum dotstructure 1100 is stacked or layered so a dark reference electricalinterconnection can be buried in a lower portion of the quantum dotstructure 1100. The thickness of the quantum dot structure may itselfprovide enough darkness for a dark measurement. In this embodiment oneelectrical interconnection 1404 is close to the radiation 1000 and other(i.e. dark reference) is farther from radiation 1000. The closerinterconnection is close to the photosensitive part of quantum dotstructure 1100. The dark interconnection is farthest from radiation1000, which is farther from the photosensitive layer of the quantum dotstructure 1100. Embodiments use an electrical scheme to sense thedifference between the two structures. In embodiments, the twoelectrical interconnections are at or near the same potential to preventtop to bottom conductivity.

Embodiments involve a self-referenced dark reference. This may involvetwo levels of contacts: one level close to the radiation 1000 andanother farther from radiation 1000. The contact closest to radiation1000 is close to photosensitive part of film and the farthest fromradiation 1000 is farther from photosensitive film. An electrical schememay be employed that senses the difference between the two structures.Under no illumination (i.e. in the dark) the resistors associated withthe dark references and the active materials have the same resistance. Acircuit is configured (e.g., a Wheatstone bridge, etc.) in which theoutput signal is related to the difference in resistances between theseparate referenced electrical interconnects. Thus, under darkconditions, the signal output is zero. Under illumination, moreradiation 1000 is absorbed by the photodetector which is struck first bythe radiation 1000, since following radiation 1000 passage through thisfirst photodetector, the optical intensity is attenuated. As a result,the incidence of radiation 1000 changes the top, morestrongly-illuminated photodetector than it does change the bottom one.As a result, the difference in resistance between the twophotodetectors, now both illuminated, but differently-illuminated), isproportional to the optical intensity. The same signal, related to aresistance difference between the top and bottom layers, provides anoutput signal that is directly related to optical intensity.

In embodiments, multispectral quantum dot structure pixels are provided.In embodiments the multispectral nature of the pixel is provided byproviding different spectral response quantum dots within a given pixel(e.g. arranged to respond to R, G, B and IR). In embodiments themultispectral nature of the pixel is provided by providing differentspectral response quantum dots spread between different pixels (e.g. onepixel is an R response and one is B response, etc.). The separate pixelstructures could effectively mimics a pixel layout (e.g. an RGB or CMYpattern). In embodiments the multispectral nature of the pixel isprovided by providing different spectral response quantum dots spreadbetween different pixel layers.

Stacked Multilayer Pixels

Multiple layers of quantum dot structures 1100 may be verticallystacked, as described herein, to generate a multi-spectral pixel. Increating a vertically-stacked multi-spectral pixel, the upper layers mayabsorb and simultaneously detect certain wavelengths of radiation,transmitting other wavelengths for subsequent detection in lower layers.While each layer may achieve substantially complete absorption withinthe spectral region for which it is configured to be responsive, theembodiments are not so limited. Outside of this band, and within theband(s) for which lower-down layers are responsive for the detection ofradiation 1000, this upper-lying pixel should be substantiallytransmissive.

A multicolor, multilayer photodetector of an embodiment includes thefollowing components or elements, as described in detail herein, but isnot so limited: an integrated circuit; at least two optically sensitivelayers, a first optically sensitive layer and a second opticallysensitive layer, the first optically sensitive layer over at least aportion of the integrated circuit and the second optically sensitivelayer over the first optically sensitive layer; each optically sensitivelayer interposed between two electrodes, a respective first electrodeand a respective second electrode; the integrated circuit configured toselectively apply a bias to the electrodes and to read out a signal fromthe optically sensitive layers related to the number of photons receivedby the respective optically sensitive layer.

An image sensor may be produced which comprises an array of suchmultilayer photodetectors, each representing a pixel, wherein theelectrical signal in each layer within each pixel region is independentregistered and is conveyed to other regions of the integrated circuit.In embodiments, such a multilayer photodetector may accomplish colorsensing by using a top layer that is sensitive to blue light, having atypical cutoff of absorption at approximately 490 nm; and a lower layerthat is sensitive to blue and green light, having a typical cutoff ofabsorption at approximately 560 nm.

While the lower layer is sensitive to both blue and green light, thestacked photodetector of an embodiment can be configured such that thetop layer substantially absorbs blue light. The light impinging on thelower photodetector is therefore substantially lacking in blue light. Asa result the photocurrent produced in the lower photodetector will bedetermined predominantly by the intensity of green light striking thestacked pixel.

In embodiments, sensing of red and near-infrared light may beaccomplished with a conventional pinned silicon photodiode integratedwithin the CMOS integrated circuit.

In embodiments, a multilayer photodetector accomplishes color sensingusing a structure including a top layer, a middle and a lower layer. Thetop layer is sensitive to blue light and has a typical cutoff ofabsorption at approximately 490 nm. The middle layer is sensitive toblue and green light and has a typical cutoff of absorption atapproximately 560 nm. The lower layer is sensitive to blue and green andred light, and has a typical cutoff of absorption lying beyond 650 nm,typically at 650 nm, 700 nm, or 750 nm.

While the middle layer is sensitive to both blue and green light, thestacked photodetector may be configured such that the top layersubstantially absorbs blue light. The light impinging on the middlephotodetector is therefore substantially lacking in blue light. As aresult the photocurrent produced in the middle photodetector will bedetermined predominantly by the intensity of green light striking thestacked pixel.

Similarly, while the bottom layer of this embodiment is sensitive toboth blue and green and red light, the stacked photodetector may beconfigured such that the top layer substantially absorbs blue light; andthe middle layer substantially absorbs green light. The light impingingon the bottom photodetector is therefore substantially lacking in blueand in green light. As a result the photocurrent produced in the bottomphotodetector will be determined predominantly by the intensity of redlight striking the stacked pixel.

In an alternative embodiment, a multilayer photodetector accomplishescolor sensing using a structure including a top layer, a middle and alower layer. The top layer is sensitive to blue light, for example, andhas a typical cutoff of absorption at approximately 490 nm. The middlelayer is sensitive to blue and green light, having a typical cutoff ofabsorption at approximately 560 nm. The lower layer is sensitive to blueand green and red and infrared light, and has a typical cutoff ofabsorption lying beyond 700 nm, 800 nm, 900 nm, 1000 nm, 1300 nm, 1650nm, 3 um, or 5 um wavelength.

In systems constructed to include and use such stacked pixels, aninfrared cutoff filter may be selectively deployed such that, at highlight, and for the purposes of visible color imaging, the infraredfilter prevents infrared light from impinging on the sensor layer. Underlow-light, including nighttime, conditions, the filter is removed fromthe optical path, such that the bottom layer provides a combination ofred and infrared sensitivity. Embodiments include imaging systems whichachieve low-light sensitivity; which achieve imaging using activeinfrared illumination; and/or which achieve imaging based on thenightglow emissions that provide substantially infrared illumination ofa scene.

In other alternative embodiments, a multilayer photodetectoraccomplishes color sensing, including infrared sensing, through use of astructure including a top layer, an upper middle layer, a lower middlelayer, and a lower layer. The top layer is sensitive to blue light, andexhibits a typical cutoff of absorption at approximately 490 nm. Theupper middle layer is sensitive to blue and green light, and exhibits atypical cutoff of absorption at approximately 560 nm. The lower middlelayer is sensitive to blue and green and red light, and exhibits atypical cutoff of absorption lying beyond 630 nm, typically at 630 or650 or 670 or 700 nm. The lowest layer is sensitive to blue and greenand red and infrared light, having a typical cutoff of absorption lyingat 800 nm, 900 nm, 1000 nm, 1300 nm, 1650 nm, 3 um, or 5 um wavelength.

Embodiments include imaging systems which achieve low-light sensitivity;which achieve imaging using active infrared illumination; and/or whichachieve imaging based on the nightglow emissions that providesubstantially infrared illumination of a scene.

The optically sensitive materials making up some or all of the layers ofa multilayer pixel can include photoconductive photodetectors havinggain. They may employ films made from colloidal quantum dots in whichone carrier type is the flowing carrier, and the other carrier type issubstantially blocked, or trapped, or both. For example, if PbS (leadsulfide) is employed as a colloidal quantum dot materials system, it maybe that holes serve as the flowing carrier; whereas electrons aretrapped. Organic ligands may be employed at various phases in materialsand device fabrication in order to provide a stable colloid when theparticles are in the solution phase. Some or all of these organicligands may be removed or replaced during processing, both insolution-phase processes and also in the formation of solid films. Suchmodification of the presence of ligands may be exploited to improveand/or control the flow of charge carriers in the devices.

Semiconductor nanoparticles may be employed whose dimensions, along atleast one spatial axis, are comparable to or less than the Bohr excitonradius of bound electron-hole pairs within the nanoparticle. Forexample, in PbS, the Bohr exciton radius is typically reported in therange 18-25 nm. When the nanoparticle diameter is chosen, typicallythrough synthetic conditions at the time of nanoparticle manufacture, tolie below the Bohr exciton radius, the effective bandgap of theresulting set of colloidal quantum dots may lie well in excess of thebulk bandgap of the constituent semiconductor. For example, in PbS, thebulk bandgap is approximately 0.4 eV. When nanoparticles ofapproximately 8 nm diameter are produced, the absorption onset may liecloser to 0.7-0.8 eV. When nanoparticles of approximately 4 nm diameterare produced, the absorption onset may lie closer to 0.9-1.0 eV. Whennanoparticles of approximately 0.5-2 nm diameter are produced, theabsorption onset may lie in the range 2-3 eV. It is worth noting that,in this example, the effective bandgap of the quantum-confined materialmay be more than double (when measured in energy units, electron volts,eV) the bulk bandgap of the bulk material of which the nanoparticles arematerially constituted.

In embodiments, the multiple (two-or-more) stacked photosensitive layersdescribed above, each having a different effective bandgap, may comprisesemiconductor materials having the same composition; but the diameter ofthe particles in the upper layer(s) will have smaller diameters thanthose in the lower layer(s) in order to achieve a shorter-wavelengthcutoff in the upper layer(s) compared to in the lower layer(s).

In embodiments, the multiple (two-or-more) stacked photosensitive layersdescribed above, each having a different effective bandgap, may comprisesemiconductor materials having a generally differing composition, andalso a generally differing diameter. In producing a three-color visible(blue, green, red) pixel, for example, the top (blue) layer may beconstituted of In2S3 having diameter 2 nm; the middle (green) layer maybe constituted of In2S3 having diameter 4 nm; and the bottom (red) layermay be constituted of PbS having diameter 2 nm.

In embodiments that employ different materials in some of the layers,the nanoparticles in the lower layers may thus have smaller bandgaps,but also smaller diameters, than those in the upper layers.

Examples of materials making up the optically sensitive layers includePbS, PbSe, In2S3 In2Se3, Bi2S3, Bi2Se3, InP, Si, Ge. Nanoparticlediameters may typically range from 0.5 nm to 10 nm.

Highly monodispersed colloidal quantum dots are often reported toexhibit an excitonic peak in the absorption spectrum, wherein a localmaximum (often a pronounced one) is observed in the absorption spectrumat energies approximately 0.05-0.5 eV above the absorption onset. Thisfeature may assist in providing the color discrimination desired herein.In embodiments, no defined local maximum in the absorption spectrum nearits onset may be observed. In embodiments, only an absorption edge maybe observed.

In embodiments, one or more of the layers in the multilayerphotodetector may provide photoconductive gain. This may be accomplishedthrough the use of a layer that substantially absorbs light in thespectral regime of interest (for example, blue in a top layer)—forexample, the absorbance (also known as quantum efficiency) in thisspectral regime may exceed 50%; and through the use of a medium in whichthe transit time for the flowing carrier (such as holes) is less thanthe lifetime of that carrier; and in which the other carrier (such aselectrons) either exhibits a low mobility (much lower than that of theflowing carrier, typically 10× or a greater multiple lower mobility) oris blocked (such as by using an electron-blocking layer) or both.

In embodiments, photoconductive gain may be equal to unity or greater.When combined with absorption of 50% or greater, the number of electronsflowing per second through the pixel may exceed 0.5 times the number ofphotons impinging on the pixel per second. For light at the wavelength550 nm, for example, this corresponds to a Responsivity in excess of0.22 A/W.

In embodiments, the responsivity may be of at least 0.4 A/W. Typicaldesired ranges of Responsivity range from 0.4 A/W to 10 A/W.Photoconductive gains resulting in responsivities of 100 A/W or 1000 A/Whave been shown experimentally as reported herein; and may inembodiments be employed.

Such responsivities may be achieved using voltage biases of 0.5 V or 1 Vor 1.2 V or 1.5 V.

In embodiments including multiple (two-or-more) stacked photosensitivelayers, the first optically sensitive layer comprises a nanocrystalmaterial having photoconductive gain and a responsivity in the range ofabout 0.4 A/V to 100 A/V; and the second optically sensitive layercomprises a nanocrystal material having photoconductive gain and aresponsivity in the range of about 0.4 A/V to 100 A/V that is greaterthan the first photoconductive gain; and the multilayer photosensorfurther comprises circuitry to generate image data, including circuitryconfigured to compensate for the difference in photoconductive gainbetween the first optically sensitive layer and the second opticallysensitive layer. In embodiments, the renormalization for the differinggains in the different optically sensitive layers may be achieved usingan image sensor processor and/or using software.

In embodiments, the materials compositions and layer thicknesses of thetwo-or-more optically sensitive layers in the stacked pixel may beselected such that the responsivities in the color ranges of interest toeach optically sensitive layer may be rendered approximately equal invalue. For example, compositions and thicknesses may be selected suchthat a top layer provides a responsivity of approximately 3 A/W inmiddle of the blue; the middle layer provides a responsivity ofapproximately 3 A/W in the middle of the green; and the bottom layerprovides a responsivity of approximately 3 A/W in the middle of the red.

In embodiments, the materials compositions and layer thicknesses of thetwo-or-more optically sensitive layers in the stacked pixel may beselected such that the product of Absorbance and Photoconductive Gainwithin each optically sensitive layer may be rendered approximatelyequal in value. For example, compositions and thicknesses may beselected such that a top layer provides an Absorbance*PhotoconductiveGain product of approximately 6 in the middle of the blue; a middlelayer provides an Absorbance*Photoconductive Gain product ofapproximately 6 in the middle of the green; and a bottom layer providesan Absorbance*Photoconductive Gain product of approximately 6 in themiddle of the red. In embodiments, the absorbance of each layer willexceed 70%, and may range from 70%-95%, at the peak of the spectralregime of interest. For example, the Absorbance of a top layer may beapproximately 80% in the middle of the blue; the Absorbance of a middlelayer may be approximately 80% in the middle of the green; and theAbsorbance of a bottom layer may be approximately 80% in the middle ofthe red. In embodiments, the Photoconductive Gain of each layer may besimilar, such as taking on a value of 7.5, or another value within arange of approximately 1-10.

In embodiments, an image sensor may be realized using an array ofstacked pixels wherein at least one pixel in the array is substantiallyobscured, preventing the incidence of light. Such substantially obscuredpixel or pixels may be termed ‘black pixels.’ The current flowing ineach photosensitive layer of the black pixel will thus correspondapproximately to the dark current associated with that photosensitivelayer. If the photosensitive layers making up the stacked pixels aremade to be of substantially similar thickness, carrier density, lateraldimensions, and carrier transport properties across the array, then thedark current associated with each sensitive layer, as provided by theblack pixel(s), may be used as a basis to subtract off the effect of thedark current in the (non-obscured) light-sensing pixels making up theremainder of the array. Simple dark-current-subtracting analog circuitsmay be employed to remove the offset, or black level, associated witheach photosensitive layer.

In embodiments, an upper layer may be more strongly absorbing (per unitlength, with absorbance per unit length measured in units of cm-1) inits wavelength of interest than a lower layer. For example, an upperlayer may absorb in the blue with an absorption of alpha=60,000 cm-1,while a lower layer may absorb in the green with an absorption ofalpha=50,000 cm-1. To absorb approximately 80% of blue light, the upperlayer may thus be made to be approximately 250 nm thick. To absorbapproximately 80% of green light, the lower layer may thus be made to beapproximately 300 nm thick. In this example, the dark currents flowingin the upper and lower layers may thus be generally different. If biasedto the same potential difference, and if constituted of materials havingessentially similar mobilities and carrier densities, then if thebiasing electrodes are configured at a distance equal to the materialthickness (such as in a vertical pixel) then the thinner upper layer mayprovide a higher dark current; or, if the biasing electrodes areconfigured along an axis perpendicular to the film thickness (such as alateral electrode configuration), then thinner upper layer may provide alower dark current. In the former case, a black-level subtractioncircuit will subtract a larger current from signals corresponding toupper-layer photosensitive regions; whereas in the latter case, ablack-level subtraction circuit will subtract a smaller current fromsignals corresponding to upper-layer photosensitive regions.

Embodiments include stacked pixels wherein at least one of the opticallysensitive layers is employed to produce an essentially unipolar device.In the unipolar device, the transport of one carrier type (electrons orholes) predominates over the transport of the other type (holes orelectrons). For example, in PbS photoconductive colloidal quantum dotdetectors described herein, holes may be the flowing carrier and mayhave a mobility of at least 10× greater than electrons. For example, thehole mobility may equal 1E-4 cm2/Vs while the electron mobility may beinferior to 1E-5 cm2/Vs.

Embodiments include the use of at least one optically sensitive layerthat consists of substantially monodispersed nanoparticles. For example,an optically sensitive layer may consist substantially of nanoparticleshaving average diameter 1.5 n, and ranging in diameter from 1-2 nm.

Embodiments include the use of at least one optically sensitive layerthat consists of nanoparticles whose cores are in physical proximity(separated by less than 0.5 nm) and substantial electrical communicationwith one another (achieving hole mobility of 1E-5 cm2/Vs or greater).

Embodiments include the use of at least one optically sensitive layerthat consists of nanoparticles whose cores are bridged by bidentatelinker molecules (such as ethanedithiol or benzenedithiol).

Embodiments include the use of at least one optically sensitive layer inwhich the dark current density is in the range of 10-500 nA/cm2 andwhich provides a noise-equivalent exposure of between 3 pJ/cm2 and 30pJ/cm2.

Embodiments include electrode configurations wherein each opticallysensitive layer comprises a continuous film of interconnectednanocrystals in contact with the respective first electrode and therespective second electrode; wherein the second electrode is at leastpartially transparent and is positioned over the respective opticallysensitive layer; and wherein the flowing-carrier transit time is lessthan the carrier lifetime, a.k.a. the persistence time. For example, theflowing-carrier transit time may be less than 15 milliseconds; while thecarrier lifetime or persistence time may be approximately 30milliseconds. In general the flowing carrier lifetime may range from 1microsecond to 30 milliseconds; and the carrier lifetime or persistencetime may range from 2 microseconds to 60 milliseconds.

FIG. 3 s is a stacked multilayer pixel having an electrode configurationwherein each respective first electrode (C1) is positioned laterally toat least a portion of the respective second electrode (c2), under anembodiment. Put another way, the region of physical and electricalcontact between a first electrode (C1) and the portion of film (QF1)that this electrode touches is at substantially the same elevation(measured relative to the top surface of the silicon chip, for example)as the region of physical and electrical contact between a secondelectrode (C2) and the portion of film that this electrode touches.

FIG. 3 r is a stacked multilayer pixel having an electrode configurationwherein one common electrode (CC) extends in the vertical direction overthe height of more than one of the photosensitive layers (QF1+QF2); andwherein separate, electrically independent, electrodes (C1 AND C2) areused to bias and collect current substantially independently from thephotosensitive layers (QF1 AND QF2), under an embodiment. Embodimentsinclude a current blocking layer (B) which substantially preventselectrical crosstalk between the layers (QF1 and QF2).

FIG. 3 u and FIG. 3 v is a side and top view, respectively, of a stackedmultilayer pixel having an electrode configuration wherein a commonelectrode (CC) is disposed around an electrode (C1) in electricalcontact with a first photosensitive layer (QF1); and the commonelectrode (CC) is disposed around an electrode (C2) in contact with asecond photosensitive layer (QF2), under an embodiment. Embodimentsinclude those that employ an electrically insulating (Blocking) layer toprovide substantial electrical isolation between the photosensitivelayers.

FIG. 3 w depicts an image sensor, in cross-section, showing byillustration how two layers of optically sensitive material, stackedatop one another, can be independently read out electrically. 1450 isthe silicon substrate which forms part of the read-out integratedcircuit and the eventual image sensor. 1451 is a metal layer within theinterconnect stack that connects to a bias available elsewhere on thechip. 1451 is electrically connected to 1452, the common posts thatreach up vertically to provide one of the electrodes contacting theoptically sensitive layer. In this particular instance, 1452 is inelectrical communication with both quantum film layers 1455 and 1456:thus it provides a contact common to each layer. 1453 is one pixelelectrode that provides electrical communication between the lowerquantum film layer 1455 and circuitry on the substrate 1450. 1454 isanother electrically independent pixel electrode that provideselectrical communication between the upper quantum film layer 1456 andcircuitry on the substrate 1450. It is shown visually that the post 1454is clad on its sides by an insulating layer which prevents significantelectrical communication between 1454 and the lower optically sensitivelayer 1455. In this way electrical communication among pixel electrodesand optically sensitive layers is unique to the pair {1453, 1455} andindependently {1454, 1456}. As a result the light level absorbed in 1456is communicated to its corresponding read-out circuit substantiallywithout regard for the light level incident on 1455; and, similarly, thelight level absorbed in 1455 is communicated to its corresponding andseparate read-out circuit substantially without regard for the lightlevel incident on 1456. It will be understood that 1456 and 1455 maygenerally be made using materials having different spectra of opticalsensitivity. 1456 could for example be made of the same constituentsemiconductor material, but smaller-diameter, semiconductor quantum dotsthan 1455, in which case 1456 would absorb and sense higher-energyphotons, while 1455 would absorb and sense primarily lower-energyphotons. Because of the substantial electrical independence of theirconnection to their respective read-out circuits, the spectralinformation absorbed in 1456 versus the spectral information absorbed in1455 can be substantially distinguished from one another.

Embodiments include electrode configurations wherein the respectivesecond electrode for the first optically sensitive layer and the secondoptically layer comprises a mesh between the vertically stacked pixeland an adjacent vertically stacked pixel. Embodiments include an arrayof vertically stacked pixels with multiple layers each having a firstelectrode, a mesh interposed between the vertically stacked pixels andconfigured to provide a common electrode for each layer in thevertically stacked pixels.

Embodiments include a photosensor array wherein the fill factor is atleast 80%, with typical range being 80%-100%. Fill factor is taken tomean the ratio of the unobscured, absorbing area of each pixel to thetotal area of each pixel, but can have other meanings as appropriate andunderstood by one skilled in the art.

Embodiments include a system-on-chip wherein the photosensor array iscombined with circuitry to compensate for different properties—such asdark current and responsivity—for different optically sensitive layers.System-on-chip implementations are described elsewhere herein. Thecircuitry combined with the sensors of an embodiment can include anycircuitry appropriate to a chip or application implementation of thesensor. For example, embodiments include circuitry (analog, digital, ora combination thereof) that implements a demosaicing algorithm to reporta corrected color matrix (e.g. blue, green, red) for a particularcomposite stacked pixel in view of the Responsivity and Absorbancespectrum of each photosensitive layer in the stack. As another example,embodiments include circuitry (analog, digital, or a combinationthereof) that subtracts from the electrical signal reported from a lowerpixel an electrical signal that is related to the electrical signalreported from an upper pixel, or upper pixels, in order to reduce colorcrosstalk in the extracted color signals.

Photodetectors compatible with video frame rates, and possessingphotoconductive gain, are now discussed. Embodiments described hereininclude a photoconductive photodetector in which substantially a singlechemical species has associated with it a substantially single energydepth and thus, at a given temperature, a substantially single trapstate lifetime, and thus a substantially single temporal componentassociated with the rise and fall of photocurrent during incidentoptical transients. Embodiments include photoconductive photodetectorswhere the single chemical species is PbSO3 (lead sulfite); the singleenergy depth is approximately 0.1 eV; at room temperature thesubstantially single trap state lifetime is ˜30 milliseconds; thesubstantially single temporal component associated with the rise andfall of photocurrent is ˜30 milliseconds. In embodiments the followingare not substantially included into the photoconductive medium: leadsulfate PbSO4, having depth 0.3 eV or greater, and having transientcomponent of order seconds; lead carboxylate, having depth 0.2 eV orgreater, and having transient component of order half a second or more.

Methods used to obtain and characterize certain embodiments of thephotodetector 1400 will now be described. A typical synthesis of PbS NCswith an excitonic peak between 700 nm and 800 nm may involve injectionof 2.0 mmoles of bis(trimethylsilylsulfide) into a reaction flaskcontaining 4.0 mmol of lead oxide (0.9 g), 9.5 mmol of oleic acid (2.67g), and 18.8 mmol of octadecene (4.73 g) at 80° C. After the injectionthe reaction may be quenched by moving the flask to an ice-water bath.The synthesis may be carried out under inert conditions using a Schlenkline. The final PbS oleate-capped NCs may be isolated from any remainingstarting materials and side products by precipitating with acetone. Theprecipitate may then be redispersed in toluene and precipitated againwith acetone. The final nanocrystals may be redispersed in toluene fordevice fabrication.

Since bulk PbS may have a bandgap of approximately 0.4 eV, it may benecessary to increase dramatically the degree of quantum confinement inthe quantum dot materials 200 to make the visible-only colloidal quantumdot photoconductive detector 1400 of the embodiment. An improvement inthe synthetic procedure may enable the synthesis of quantum dots 1200with absorption onset below 800 nm, as described herein. FIG. 3 i(a) mayillustrate the absorption spectrum of the resultant quantum dots. Asseen in FIG. 3 i(b), the nanoparticles may have diameters of 3 nm andexhibit faceting. As synthesized, these nanocrystals may be stabilizedwith oleic acid, a configuration expected and observed to impede carriertransport due to the oleate ligand's long insulating chain. Exchangingto shorter ligands such as butylamine may result in a dramatic increasein conductivity. Whereas in the case of larger 4-6 nm nanoparticles,monodispersity and excitonic features may be preserved after ligandexchange in solution phase, in the small nanocrystal case, the proceduremay lead, instead, to the formation of nanostrings (FIG. 3 i(c)) aspreviously seen for PbSe nanoparticles (Cho, K. S. Talapin, D. V.Gaschler, W. Murray, C. B. Designing PbSe Nanowires and Nanoringsthrough Oriented Attachment of Nanoparticles Journal of the AmericanChemical Society 127, 7140-7147 (2005)); and, more problematically, aloss of an abrupt absorption onset (dashed curve, FIG. 3 i(a)) resultingfrom irreversible aggregation.

Thus, an approach that would instead preserve a sharp, short-wavelengthabsorption onset may be preferred. Ligand exchange in the solid state,once thin films may already be formed, may limit the number ofnanocrystal reattachment sites and dramatically improve conductivitywithout dramatically altering quantum-confined energy levels. PbSnanocrystals dispersed in toluene may be spincoated onto glasssubstrates with gold interdigitated electrodes with a 5 μm spacing(shown in FIG. 3 m) to form a solid state film with thickness of 360 nm.The film may then be treated in a mixture of 20% butylamine inacetonitrile over two days. Following this solid-phase ligand exchange,the film may exhibit conductivity with dark current density 600 μA cm⁻²at applied field of 20 V μm⁻¹ (shown FIG. 3 n). Untreated samples orsamples treated with acetonitrile alone may not exhibit measurableconductivity.

Quantum dots may, for example, be synthesized to provide a typicalabsorption maximum of approximately 730 nm. The fabrication may becarried out as a batch process. These nanomaterials may be soluble inorganic solvents such as chloroform, toluene or tetrahydrofuran. Thesynthesis may be divided into steps. The first two steps require the useof an inert atmosphere by using a Schlenk technique and N2 glove box.One step involves preparation of Pb precursor, such as Pb oleatedissolved in a mixture of 1-octadecene and oleic acid. Another stepinvolves preparation of S precursor, such as Bis(trimethylsilyl)sulfidedissolved in 1-octadecene. A further step includes fast injection of(2.) into (1.) to form PbS QD in a single event. When the Pb precursorhas reached a temperature well above room temperature, the S precursoris entirely injected within a few seconds through the septum. Thesolution turns from a colourless to a dark orange/black solution. Afurther step includes purification and storage. The reaction solution ispoured into the acetone; a brown suspension with black precipitate isformed, leaving a black residue on the bottom of the flask. The entirebeaker content is centrifuged. After centrifugation the clear/lightbrown supernatant is removed. Chloroform is used to bring the remainingprecipitate into solution. A Vortex mixer helps to completely dissolvethe nanomaterials into chloroform. In order to wash the nanoparticlesand remove unwanted by products, the chloroform solution is brought intoa beaker with fresh acetone (four fold volume of the chloroform/QDsolution). A brown suspension with dark brown precipitate is formed. Afinal centrifugation step is carried out, and the clear supernatant isseparated from the dark brown residue. The remaining nanomaterials aredried for several hours in vacuum.

In many embodiments, the QDs are fabricated using known techniques, butin substantially inert, anhydrous environments, e.g., environments thatare substantially free of water and oxygen. Syntheses may be performedusing Schlenk line methods in which ambient gases such as oxygen andwater in the air are excluded from the system, and the syntheses areinstead performed in the presence of substantially inert gases such asnitrogen and/or argon, or in a vacuum.

Quantum dot 1200 synthesis may be affected by a number of factors.Temperature may affect quantum dot 1200 synthesis. For example, thetemperature of the synthetic materials may be modified by placement inan ice bath. The temperature may also be modified by placing thesolution into a cooling tube with an evacuated flask on one end and ablocker with pressure on one side that pushes the solution through. Thesolvent type may affect quantum dot 1200 synthesis, such as for example,a hydrous solvent versus an anhydrous solvent. After synthesis, thequantum dots 1200 may be precipitated (through the additional ofmethanol, acetonitrile, ethyl acetate, isopropanol, propanol), andcentrifuged. The supernatant may be decanted and excessprecipitating-nonsolvent (listed in previous sentence) may be evaporatedor otherwise removed.

Means of realizing solid-state devices using colloidal quantum dots suchas those described above is now discussed. Solution-phase-dispersedcolloidal quantum dots provided through syntheses described herein maybe formed into photodetectors using processes such as the following. Asolution-phase exchange is carried out to replace as-synthesized ligands(such as oleic acid) with shorter ligands (such as ethanethiol,butanethiol, hexanethiol, dodecanethiol, or combinations thereof). Thismay aid in achieving efficient transport of charge carriers in theoptically sensitive layer and thus in providing for useful levels ofphotoconductive gain. A film may be produced by spin-coating quantumdots from solution onto a substrate, such as a silicon integratedcircuit. The film may be further treated such as through exposure toshort ligands in solution (such as ethanethiol, propanethiol) and/orthrough exposure to linkers (such as ethanedithiol, butanedithiol,hexanedithiol).

In an embodiment, quantum dots 1200 may be post-synthetically processed.Post-synthetic processing may involve precipitation and redispersion.Post-synthetic processing may involve drying the quantum dots 1200 whichmay have been previously soaking, redispersing them in a solvent,filtering the solution, concentrating the solution, then spinning thesolution or depositing the quantum dots 1200 in another manner asdescribed herein. This process may result in a concentration of aparticular size of quantum dots 1200. Redispersion may involve soakingthe precipitated quantum dots 1200 in a solvent, such as butyl amine,toluene, and the like to provide for ligand exchange, as describedbelow. Non-toluene soaks may provide faster redispersion. After ligandexchange, the quantum dots 1200 may need to be re-precipitated andredispersed into a solvent such as chloroform. To prepare the quantumdots 1200 for spinning, they may need to be dried, re-filtered,re-dispersed, and concentrated down. The quantum dots 1200 may need tomature for a time period, such as in the range of five days.

In an embodiment, there may be additional quantum dot 1200post-synthetic solution-based treatments.

Referring to FIG. 2 a, the synthesized quantum dot 1200 may includeattached ligands 1225. As shown in FIG. 2 a, attachment of the ligand tothe quantum dot 1200 may be through a ligand functional group 1250.Referring to FIG. 2 b, vials containing variations of quantum dots areshown. The variations result in differences in radiation emission, asdepicted in FIG. 2 d for visible light. Referring to FIG. 2 c, an SEMimage of a single quantum dot 1200 and an array of quantum dots 1200 isshown.

In some embodiments, the QDs include any one or combination of PbS,InAs, InP, PbSe, CdS, CdSe, ternary semiconductors, and a core-shelltype semiconductors in which the shell is one type of semiconductor andthe core is another type of semiconductor. For example, the ternary QDsmay be In_(x)Ga_(1-x)As nanocrystals or (Cd—Hg)Te nanocrystals. Forexample, the core-shell quantum dot nanocrystals may be ZnSe(PbS),ZnS(CdSe), ZnSe(CdS), PbO(PbS), or PbSO₄(PbS).

In embodiments, before depositing the QD precursor layer on theintegrated circuit or substrate, the QDs are ligand exchanged tosubstitute the as-fabricated ligands with pre-selected ligands, e.g.,ligands that are considerably shorter than the as-fabricated ligands.The pre-selected ligands are selected to be sufficiently short to enablecloser packing of the QDs in the precursor layer. Closer packing allowsthe QDs to fuse together in a subsequent step, thereby greatlyincreasing the electrical conductivity between the QDs. The pre-selectedligands may also be selected to be relatively volatile, so that they canbe vaporized during a subsequent step to provide a film consistingmainly of QDs and being substantially free of ligands. This allows theQDs to get much closer to each other, which may enhance the conductivityin the final device. For example, the QDs may be fabricated with a firstset of ligands with carbon chains that are more than 10 carbons long;the first set of ligands is then substituted with a second set ofligands with carbon chains that are between 1-10 carbons long. In somecircumstances, the ligands of the second set of ligands are less thanabout 1 nm long. This can bring the QDs closer, e.g., more than 50%closer, more than 75% closer, or even more than 90% closer, than theycould get before ligand exchange. The second set of ligands maygenerally have an affinity for attachment to the QDs that is at leastcompetitive with the affinity of the first set of ligands to attach tothe QDs, otherwise the first set of ligands may not sufficientlyexchange with the first set of ligands. The second set of ligands mayalso generally have an affinity for attachment to the QDs which allowsthem to be removed during a later step. This affinity is related to theend functional group on the ligand, which is illustrated in FIG. 2 a.Amines, thiols, carboxylates, and sulfones, among other end functionalgroups, many of which will have free electron pairs, are generallysuitable for use in the second (pre-selected) set of ligands.

In embodiments, the ligand exchange involves precipitating theas-synthesized QDs from their original solution, washing, andredispersing in a liquid that will dissolve and thus dissociate theoriginal ligands from the outer surfaces of the QDs, and which either isor contains the ligands to be substituted onto the QDs. In someembodiments the liquid is or includes primary, secondary, ortertiary-butylamine, pyridine, allylamine, methylamine, ethylamine,propylamine, octylamine, or pyrrolidine or a combination of theseorganic solvents, which substitute the ligands previously on the QDs. Inother embodiments, the liquid is or includes pyridine, which substitutesthe ligands previously on the QDs. Leaving the QDs in this liquid forbetween 24 and 120 hours either at room temperature or at an elevatedtemperature is generally sufficient for ligand exchange, although insome circumstances longer or shorter times will be sufficient. In anillustrative example, the ligand exchange process was performed under aninert atmosphere to prevent the QDs from oxidation. QDs having oleateligands and dissolved in methanol were precipitated, dried, andredispersed in n-butylamine at a concentration of 100 mg/ml(nanocrystals by weight/butylamine by volume). The solution was left for3 days under inert conditions. The oleate ligands had a length of about2.5 nm, and the exchanged butylamine ligands had a length of about 0.6nm, bringing the QDs to about 25% of their original distance from eachother.

In embodiments, two or more types of QDs are separately fabricated incoordinating solvents. Each kind of QD is then precipitated, washed, anddispersed in a liquid that is or contains the ligands to be substitutedonto the QDs. This exchanges the ligands on the two or more types of QDsas discussed above. Then the two types of QDs are mixed in solution tocreate a heterogeneous QD mixture, which is spin-cast or otherwisedeposited as thin films on a substrate to form a heterogeneous QDprecursor layer. The order in the heterogeneous QD precursor layer iscontrolled through separate selection of QD size and ligand for eachtype of QD and additional treatment with solvents and heating.

Examples of ligands include amine-terminated ligands,carboxyl-terminated ligands, phosphine-terminated ligands and polymericligands. The amine-terminated ligands may include any one or combinationof pyridine, allylamine, methylamine, ethylamine, propylamine,butylamine, octylamine, and pyrrolidine. The carboxyl-terminated ligandsmay include any one or combination of oleic acid, stearic, capric andcaproic acid. The phosphine-terminated ligands may include guanosinetriphosphate. The ligand may be one or more of DNA, an oligonucleotide,a polymer such as polythiophene or MEH-PPV, or an oligomer such asoligothiophene. As mentioned above, it can be useful to substitute shortand volatile ligands, e.g., pyridine, allylamine, methylamine,ethylamine, propylamine, butylamine, octylamine, or pyrrolidine, ontothe QDs so that the QDs can be brought into closer proximity in latersteps.

After the QDs are fabricated and ligand-exchanged, e.g., as describedabove, they may be deposited onto a substrate such as an integratedcircuit. This forms a “QD precursor layer,” which may be subsequentlyprocessed to form a finished QD layer for use in a device. Both the QDprecursor layer and finished QD layer may be used interchangeably withthe term quantum dot materials 200. In an embodiment, quantum dotmaterials may exhibit one or more of uniformity, ease of integration,low cost, stackability, monolithic integrability, photoconductivephotovoltaic gain, temperature invariance, low noise, high sensitivity,high dynamic range, mix and match capabilities, customizability ofsensors, spectral extensibility, and the like. Quantum dots may beprocessed to form quantum dot materials. Quantum dots may be processedto form a quantum dot solution. Processing may involve a number offactors, such as temperature, time, reagents, agitation, atmosphericmakeup and pressure, and the like. The quantum dots may be colloidal.The quantum dot materials may comprise a film. The film may be formed byone or more of spin coating, puddle casting, electrodeposition, vapordeposition, air brush spraying, growth from solution, hydrophobicsystems, acceleration/evaporation in gas phase, photocopying, ink jetprinting, and the like. The film may be patterned. The film may becontinuous or discontinuous. The film may be monolithic ormulti-layered. The film may be of a particular thickness. The film maycrack or not crack. The film may undergo post-film formation treatment.The film may undergo quantum dot materials processing. The film may bepost-processed. The film may be encapsulated.

The QD precursor layer may be formed by solution-depositing it directlyon the surface of a read-out integrated circuit or other substrate, forexample using spray-coating, dip-casting, drop-casting, evaporating, orblade-casting. Another method of depositing the QD precursor layer isspin coating the QD precursor layer, which once spin-coated onto thesurface may be further processed to form the optically sensitive QDlayer as described below. In many embodiments, the QD layer has athickness selected to absorb most or even substantially all of theradiation 1000 incident on it, in the wavelength region the device isintended to operate in. Typically this thickness will range betweenabout 50 nm and 2 μm, though thinner or thicker films can be usedaccording to the desired functionality of the device. Spin-coating canallow the process of covering circuitry with a QD layer to be performedat lower temperatures without vacuum processing and alignment andbonding issues. In an embodiment, quantum dot materials may be processedto form a film by spin coating. Quantum dot materials may be spin-coatedonto a substrate to form a film.

Means of measuring the response of optically sensitive layers to light,and of characterizing thereby the transduction of optical signals intothe electronic domain, are now discussed. The responsivity may bemeasured using a variety of methods. For a first method of measuringresponsivity, 2 mm radius beam from a 975 nm laser may be incident,first through a series of optical attenuators of known transmittance,and through a glass substrate, onto the device from the backside. On thetop surface, infrared-opaque interdigitated gold electrodes may beseparated by 5 μm over a 3 mm path length. The optical power incident onthe device may be obtained by integrating the intensity profile of thelaser over the unobstructed area of the device. Current-voltagecharacteristics may be acquired using an Agilent 4155 semiconductorparameter analyzer. The responsivity at different frequencies may bemeasured by electrical modulation of the laser. In a second method ofmeasuring responsivity, bias may be applied to the sample connected inseries with a 2 Mohm load resistor. Illumination may be provided by awhite light source (ScienceTech Inc. TH-2) dispersed by a Triax 320monochromator and mechanically chopped at the frequency of interest.Optical filters may be used to prevent grating overtones fromilluminating the sample. The voltage across the load resistor may bemeasured using a Stanford Research Systems SR830 lock-in amplifier. Theintensity transmitted through the monochromator at each wavelength maybe measured separately using calibrated Ophir PD-300 Si and Gephotodetectors to cover the range from 400-1600 nm. The optical powerimpinging on the active area of the detector may be taken by dividingthe active area of the device by the collimated beam area and multipliedby the total power measured with the calibrated detectors. Thephotocurrent at each wavelength may be subsequently scaled according tothis system calibration. The same setup may enable measurement ofspectral responsivity by using a variable attenuator programmed to fixthe optical power at each wavelength. The recorded photocurrent vswavelength may yield the spectral responsivity. The results of the twoaforementioned techniques may generally agree to within less than 10%.

Dark current noise in the photodetector 1400 may be measured using aStanford Research SR830 lock-in amplifier. The devices may be biasedusing batteries, and testing carried out in an electrically-shielded andoptically-sealed probe station, on a floating table to minimizevibrational noise. The reported noise current, normalized to themeasurement bandwidth, divided by the responsivity under the samemeasurement conditions may yield the noise equivalent power (NEP). Thenormalized detectivity D* may be obtained as a function of wavelength,applied bias, and center frequency by dividing the square root of theoptically active area of the device by the NEP.

The same setup as used in spectral responsivity measurement, describedabove, may be employed. The wavelength may be fixed at 830 nm and avariable attenuator combined with neutral density filters may be used tovary the light intensity from pW up to 4 μW. For higher intensities, asemiconductor laser at 830 nm may be employed to provide optical powersup to 10 mW.

Having described the methods used to obtain and characterize thisembodiment of the photodetector, certain findings relating to thephotodetector will now be described. This embodiment of thephotodetector exhibits the simultaneous attainment of sensitivity, gain,tenability, and wide dynamic range in a visible-wavelength-sensitivespin-cast photodetector. An optimally-processed photodetector mayprovide D* of 10¹³ Jones across the entire visible spectrum, comparedwith silicon photodiodes' ˜2 10¹² Jones at 970 nm and even lower in thevisible. The photodetector may exhibit photoconductive gains exceeding100 A/W. Photoconductive gains may lie between 1 and 100.

The photodetectors may be characterized for dark current, responsivity,and noise current as described in detail above. FIG. 3 j shows theoptoelectronic performance of the photodetectors. FIG. 3 j(a) exhibitsspectral responsivity and normalized detectivity. The photoconductivegain may reach a maximum at wavelength 400 nm of ˜113 A W⁻¹ at 15 Hz.For comparison, silicon photodetectors exhibit a maximum responsivity at˜970 nm which may drop in the visible. The quantum dot photodetector1400 may have an increasing responsivity at shorter wavelengths andoptimal response in the visible spectrum. With respect to sensitivity,FIG. 3 j(a) shows a direct comparison between a typical siliconphotodetector (as in Electro Optics Technology, biased silicon detectormodel ET-2000,http://www.eotech.com/store/products.php?categoryParentName=Photodetectors&categoryName=Biased+Silicon+Detectors)of area similar to the solution-processed thin-film photodetector ofthis embodiment. Across the entire visible spectra range, the quantumdot photodetector may exhibit at least an order of magnitude betternoise-equivalent power (NEP) than its crystalline silicon counterpart.

The measured noise current spectrum for the photodetector of theembodiment is shown in the inset of FIG. 3 j(b). At low frequenciesnoise current density may follow closely the responsivity curve,suggesting that the carrier traps responsible for high-gain may alsocontribute to noise, while at higher frequencies, white noise maydominate. The Johnson noise of the detector may be estimated by(4kTB/R)^(1/2) to be ˜0.9 fA Hz^(−1/2) whereas the shot noise limit(2qI_(d)B)^(1/2) is found 0.04 pA Hz^(−1/2) where k is Boltzman'sconstant, T the temperature, R the resistance of the detector in dark, Bthe noise bandwidth, q the electron charge and I_(d) the dark current.The photodetector 1400 of the embodiment may approach the shot noiselimit to within 3-dB at 80 Hz.

The quantum dot photodetector 1400 may exhibit sensitivity superior tosilicon well beyond 50 Hz, as shown in FIG. 3 j(c), where D* is plottedas function of frequency (the inset also shows the NEP versus themodulation frequency). At low frequencies (<5 Hz) the detector mayexhibit D*˜10¹³ Jones.

The trap states responsible for photoconductive gain may becharacterized. In FIG. 3 k(a), the measured responsivity as a functionof modulation frequency for a number of different optical power levelsincident on the device is shown. The responsivity of the detector maydecrease as the optical power may be increased. This may be attributedto filling of the lowest-lying, longest-lived trap states that providethe highest photoconductive gain at low intensities. This may beconfirmed by the fact that, at high intensities, the 3 dB bandwidth mayextend to higher electrical frequencies.

In order to characterize the impact of high-gain trap state filling onthe dynamic range of the solution processed detector, the dependence ofphotocurrent on optical intensity at a modulation frequency of 30 Hz maybe measured. A monotonic, though at high intensities sublinear,dependence of photocurrent on intensity over more than 7.5 orders ofmagnitude in incident intensity corresponding to over 75 dB of intensitydynamic range may be observed (FIG. 3 k(b)). The inset of FIG. 3 k(b)shows the onset of responsivity decrease due to the filling of the highgain trap states at higher intensities that may be responsible for gaincompression.

In embodiments, photodetectors having transient responses compatiblewith video applications are desired. Optically sensitive layersproviding video-compatible temporal responses, or lags, or persistencetimes, are now discussed. With reference to FIG. 4, a transient responseto modulated 1 lx 550 nm illumination at a 5V bias is shown. Themeasurements are made on colloidal quantum dot films that have beenspin-cast and treated using the methods described herein onto planarelectrode pairs. These consist of gold or other metal linear that runparallel over a length such as 0.5 millimeters, 1 millimeter, or 3millimeters. The electrodes are separated by a constant 2.5 um or 5 umgap along their entire parallel length. Measurements are taken with abias of 1 V, 5 V, or 10 V applied across the adjacent Au electrodes. Instudies of photoresponse, the illumination source is typically a greenlight-emitting diode with a spectral emission peak near 550 nm.Square-wave modulation is provided varying from 0 lux (dark) to 1 lux.This illumination level is measured at the position of incidence ontothe test pixel sample. The illumination is calibrated using a NewportOptical Power meter. Current measurements are made using Keithley model6485 PicoAmmeters. LED and sample biases are applied using Keithleymodel 2400 SourceMeters. Measurements performed in a clean nitrogenatmosphere. In the figure, the current in one such device is shown as afunction of time. During the period ˜22.4 seconds to 25.3 seconds, forexample, the illumination source is turned on at the 1 lux level. Thusthe current flowing during this interval represents the sum of darkcurrent+photocurrent at 1 lux, where the latter component may also bethought of as equal to the responsivity (in A/W) times the optical powerreceived over the active area (optical power measured in Watts). Typicalresponsivities range from 0.4 A/W to 10 A/W. During the period 20 to22.4 seconds, for example, the illumination is turned off. The currentflowing in this interval thus represents the dark current. Typicalvalues on these test structures correspond to 0.1 pA to 3 pA. In view ofthe aspect ratios of these samples, dark currents correspond to 1E-8 to2E-6 A/cm2. Spikes at 22.4 seconds, 25.3 seconds, etc. are notproperties of the photodetector but result from electrical transientsrelating to surrounding electronics and biasing circuitry and can beneglected for the purposes of the present discussion. The rise and fallof the photocurrent, ignoring these spikes, are of interest. Inphotoconductive devices, the value of the current following a turn-offtransient in illumination, will only turn off and reach the dark-currentvalue only after some persistence time. In certain photoconductivedevices having undesirably long-lived trap states, this persistence timemay be 0.1 seconds, or 0.5 seconds, or 1 second, or longer. Suchpersistence times result in ghosting or lag artifacts in both stillimages and video. The devices realized herein are photoconductive andpossess photoconductive gain; however, their persistence times are oforder 20-40 milliseconds, such that on the typical imaging timescale,the effects of this persistence are not manifest. Thus the advantages ofphotoconductive gain are obtained, but the downside of lag is avoided.

Colloidal quantum dots provide a ready means of discriminating amongdifferent spectral bands through quantum-size-effect tuning. Thefindings described herein relating to the photodetector 1400 of theembodiment illustrate sensitivity, dynamic range, and gain all betterthan typical crystalline silicon photodiodes. A simple two-color devicemay be produced by stacking a small-quantum-dot 1200, larger-bandgapphotodetector 1400 atop a large-dot, small-bandgap (exciton peak at 1230nm) device as illustrated in the inset of FIG. 3 l. The main body ofFIG. 3 l illustrates the measured spectral responsivity of each detectorin the stack. The spectral responsivity of the small-bandgap detectorprior to stacking is also shown to demonstrate the achieved suppressionof responsivity in the visible by over 10-dB at 400 nm. Thus, the valueof quantum size-effect tenability inherent to colloidal quantum dots1200 may be depicted in FIG. 3 l.

Means of forming optically sensitive layers, including on integratedcircuits capable of providing photodetector read-out, are now discussed.In an embodiment, quantum dot materials 200 may be processed to form afilm by puddle casting. Puddle casting may comprise depositing a meteredamount of quantum dot materials 200 onto a substrate and allowingsolution to evaporate. The resultant films may or may not crack.

In an embodiment, quantum dot materials 200 may be processed to form afilm by electrodeposition. Electrodeposition may involve vacuum andquantum dots 1200. Electrodeposition may be similar to xerography. Anelectropowder coating may be used to charge the quantum dots 1200. Theassembly of electropowder and quantum dots 1200 may then be placed in asystem that is similar to a photocopier. The electropowder coating mayprovide accelerating potential without the carrier gas.Electrodeposition may involve applying a voltage across an electrodecontrolled by a circuit. The circuit may be able to sense usingdeposited quantum dot materials 200. Electrodeposition may result in adetector and feedback within itself as quantum dot pixel 1800 growthproceeds. The available photocurrent for electroplating may decrease asphotocurrent from the nascent and growing quantum dot pixel 1800increases.

In an embodiment, quantum dot materials 200 may be processed to form afilm by vapor deposition.

In an embodiment, quantum dot materials 200 may be processed to form afilm by air brush spraying. Air brush spraying may involve processingfrom gas. Air brush spraying may involve entrainment in a solvent.

In an embodiment, quantum dot materials 200 may be processed to form afilm by growth from solution. Growth from solution of a film may involvecross-linking. Crosslinkers may be attached to at least a portion of asubstrate to crosslink quantum dots 1200. When the substrate withattached crosslinker is dipped into a quantum dot solution 400, thequantum dots 1200 may become crosslinked and grow at locations on thesubstrate where crosslinker was attached in a process that may besimilar to seeded crystal growth. Since growth occurs at locations wherecrosslinker has been attached, patterned film formation on a substratemay be achieved by depositing crosslinker along the substrate in apattern. For example and without limitation, a dithiol may be used as acrosslinker. The two thiol heads of the molecule may be attached to twodifferent quantum dot 1200 surfaces and therefore yield a mobilityincrease. This crosslinking process may provide photodetection withphotoconductive photovoltaic gains on the order of, such as and withoutlimitation, tens A/W and detectivity on the order of, such as andwithout limitation 10¹² Jones. There may be a significant improvement inpersisting photocurrent which may enable high performance video imagingat frame rates up to 60 Hz.

In an embodiment, quantum dot materials 200 may be processed to form afilm by a hydrophobic system. The hydrophobic system may enabledepositing a monolayer film of quantum dots. The monolayer film may bedeposited in a pattern.

In an embodiment, quantum dot materials 200 may be processed to form afilm by acceleration or evaporation in a gas phase.

In an embodiment, quantum dot materials 200 may be processed to form afilm by a photocopying method.

In an embodiment, quantum dot materials 200 may be processed to form afilm by an ink jet printing method.

Ligand exchange during film formation may apply to any film formationmethod described herein. Ligand exchange may enable improved filmformation and improved packing of quantum dots. The duration of ligandexchange may alter the films wavelength absorbance characteristics. Inan embodiment, ligand exchange may involve exchanging long, insulatingligands capping the quantum dot for short ligands, which may enable theformation of conductive quantum dot materials and highly sensitiveradiation photodetectors. Ligand exchange may occur in the solid state.Films may first be formed by solution-processing, as described herein. Anew ligand, such as and without limitation benzenedithiol ormethanethiol, may be dispersed in a solvent, such as and withoutlimitation acetonitrile, methanol, or toluene. The sample containing thefilm may be placed in the ligand-containing solvent. The ligand may bechosen to have an end functional group that competes effectively withthat of the existing ligand. For example, thiols may bind more stronglythan carboxylic group binding, such as and without limitation oleicacid, or amine binding, such as and without limitation butylamine. Forexample and without limitation, a spincoated film may be driven into aninert atmosphere or kept at ambient conditions where it may be dippedinto a bath of a mixture of acetonitrile (MeCN) and ethanethiol (ET),ethanedithiol (EDT) or benzenedithiol (BDT). Acetonitrile may be used asa solvent for the new ligand, ET, EDT, or BDT, to replace oleic acidwhile it acts as a non-solvent for the quantum dot material filmimpeding dissolution. The ratio of MeCN:ET, EDT or EDT may vary, such asand without limitation, from 1%-10%. The duration of the bath may rangefrom 10 minutes to one hour. After the bath, the film may be isolated,washed with MeCN to remove excess ET, EDT, or BDT and any remainingoleic acid, and may be dried under vacuum.

In an embodiment, ligand exchange may occur in parallel with filmformation. First, the substrate on which the film is to be formed may beimmersed in a liquid that may include a ligand which may later replacethe ligand initially on the quantum dots. The substrate may be removed,and a coating of the new ligand may remain on the sample. Films may thenbe formed through dip-coating, wherein the sample on which the film isto be deposited may be immersed in a solvent in which the quantum dots1200 are suspended. During this process, the ligand added in the firststep serves to cause the quantum dots 1200 to aggregate, in controlledfashion, onto the sample surface. This method of parallel ligandexchange and film formation may ensure that no dramatic change in thevolume of an already-formed film be imparted. Such a dramatic change maylead to film cracking. The present method may ensure the formation ofsmooth, crack-free films by parallelizing deposition and exchange.

In an embodiment, quantum dot materials may be processed to form a filmby bridging quantum dots 1200 irreversibly during the layer growth fromthe solution phase. Quantum dots may be linked together to form acontinuous film through the use of bi-dentate ligands. These linkermolecules may bind to one quantum dot with one end while the other endbinds with another quantum dot, thus producing a chain of quantum dotsthat may prevent shorting of the device. Possible bidentate ligands mayinclude dithiols, diamines, dicarboxylic acids, combinations thereof,such as ethanedithiol, thioglycolic acid, and the like. Although the endmembers of the bi-dentating ligand should have a binding ability, therest of the molecule may be of different lengths and functionality.Short molecules may be preferred as it may enable electricalcommunication between quantum dots that is not hindered by the linkermolecule. Linker molecules may be introduced to a quantum dot pixel chip(QPDC) 100 through various means. For example and without limitation, aQPDC 100 may be placed into an organic solvent containing the linkermolecule at a variety of concentrations, such as in a range from 0.1 to10%, 1%, and the like. After treating the QPDC 100 for a time frame,such as from 5-60 minutes, the QPDC 100 may then have quantum dots 1200introduced via methods as described herein, such as dip, spray, spin,and the like. The quantum dots 1200 may then bind to the linker andafter a subsequent treatment in linker, the quantum dot 1200 maycrosslink to other quantum dots 1200. Another quantum dot 1200deposition may be performed to increase the concentration of quantumdots 1200 within the QPDC 100. This quantum dot 1200 crosslinkingstrategy may produce a continuous overlayer coverage of quantum dots1200 on either a smooth or rough electrode surface.

Absorption spectra of lead sulphide QD nanocrystals as the ligands areexchanged from oleic acid to primary butylamine may reveal a shift tothe blue with increasing exchange time. TEM images exhibit the dramaticdecrease of inter-QD spacing following ligand exchange and nonsolventtreatment. When the shift is less than that associated with the removalof a monolayer of Pb atoms (roughly 170 nm), the size distributionremains roughly constant. After this point the polydispersity increases.

The QDs were precipitated, washed using a nonsolvent, redispersed inCHCl₃, and treated again using a nonsolvent (“nonsolvent” refers to amaterial that is not a solvent for the nanocrystals, but that may be asolvent for the ligands). As-grown (untreated) QD nanocrystals showwell-ordered patterns with interdot spacing determined by ligand length.Exchanged and washed QDs exhibit a drastic reduction in interdot spacingand preferential formation of clusters instead of well-ordered arrays.Prior to treatment, the nanocrystal films can be redispersed usingorganic solvents, while after treatment, nanocrystal films can no longerbe readily redispersed.

The combination of ligand exchange, nonsolvent treatment, and thermalprocessing at temperatures such as up to about 150° C. (typically) andpotentially as high as 450° C., removes at least a portion of the QDs'ligands, and enables the QDs to fuse, providing mechanically robustfilms with vastly increased electrical conductivity, as reported below.

An exemplary photoconductive photovoltaic detector was made using asingle layer of PbS QD nanocrystals spin-cast directly from a chloroformsolution onto an interdigitated electrode array. The device structure isillustrated in FIG. 7A, and is analogous to the basic device of FIG. 4B.The parallel gold electrodes are supported by a glass substrate and havea height, width, and separation of 100 nm, 3 mm, 5 μm, respectively. Thethickness of the QD layer was controlled through the concentration ofthe chloroform-QD solution and the spin-casting parameters. In studiescarried out by the inventors the thickness ranged from 100 nm up to 500nm.

The treatment of the surfaces of the QDs was an important determinant ofphotodetector performance. Devices made directly from QDs capped witholeic acid, as synthesized through an organometallic route, did notexhibit any measurable conductance, as the 2 nm-long oleate ligandinhibits carrier transport among QDs. A post-synthesis ligand exchangewas therefore used to replace the as-synthesized oleate ligands withmuch shorter butylamine ligands. To this end, the QDs were redispersedin butylamine for a period of three days. Butylamine is afour-carbon-atom chain with an amine head as the functional group toattach to the QD surface. The ligand exchange was monitored for blueshift in QD absorption resulting from a decrease in QD effectivediameter as ligands remove Pb atoms during exchange

The absorbance spectra of QD nanocrystals before ligand exchange(oleate-capped), after ligand exchange (butylamine-capped), andfollowing soaking in methanol for 2 hours to remove the butylamineligands, may be compared. The progressive blueshift across thesetreatments is consistent with surface modification following exchangeand partial surface oxidation (also confirmed by XPS and FTIR). TEMmicrographs of the nanocrystals before and after ligand exchangeindicate a reduction in inter-particle distance is attributed to thereplacement of the oleic acid ligands with butylamine ligands.

FTIR spectra of the neat solvent n-butylamine, the neat solventchloroform, and n-butylamine-exchanged QDs dispersed in chloroform maybe obtained. N-H stretching and bending vibrations are tabulated to liebetween 3200-3600 cm⁻¹ and 1450-1650 cm⁻¹ respectively. Carbonylstretching vibration of pure oleic acid is tabulated to be found at 1712cm⁻¹. FTIR measurements indicate that oleate ligands originally attachedto the PbS QDs have been replaced by n-butylamine, indicated by theabsence of carbonyl stretching vibration, a significant shift of the N-Hstretching vibrations after exchange from 3294 and 3367 cm⁻¹ (Δ=73 cm⁻¹)for n-butylamine to 3610 and 3683 cm-1 (Δ=73 cm⁻¹), and the presence ofN-H bending vibrations for the n-butylamine exchanged sample.

FTIR spectra may be obtained for inert-exchanged ligand-exchanged QDswith butylamine ligands before and after methanol wash, whichsubstantially removes the ligands from the QDs. Following methanol wash,features attributable to butylamine (1400, 1126, 989, 837, and 530 cm⁻¹)are much less pronounced. N-H stretching vibrations are again much lesspronounced following methanol wash.

Spectra obtained by X-ray photoelectron spectroscopy (XPS) may be takento confirm the material modifications that occur to the PbS QDsthroughout various processing steps. After background subtraction, thebinding energy was reference to the C1s hydrocarbon line at 285.0 eV.The curves were fitted by applying Gaussian-Lorenzian functions and theatomic ratios were obtained by integrating the areas under the signals.The nanocrystals immediately after exchange to butylamine ligandsdemonstrate a S2-peak at 160.7 eV corresponding to lead sulfide. No leadsulfate (PbSO₄) signal was detected. Nanocrystals that were precipitatedin air exhibit an SO₄ ⁻² at 167.5 eV characteristic of PbSO₄ formation.This oxide may be associated with the role of barrier to conductionamong nanocrystals. The ratio of PbS/PbSO₄ for this case was found to beabout 3.4:1. XPS of the inert-precipitated QDs after methanol soakingexhibits also formation of lead sulfate. The PbS/PbSO₄ ratio in thiscase was 18.6:1. Further annealing of this film in air at 120° C. for 1hour dramatically increased the amount of sulfate and the PbS/PbSO₄ratio was 2.44:1.

FTIR spectra may be taken of ligand-exchanged QDs precipitated in inertconditions (butylamine-called QDs) and precipitated in air-ambientconditions (oxidize-then-neck QDs). The inert-precipitated exchanged QDlayer after 2 hours of methanol wash (neck-then-oxidize QDs) may becompared. The broad feature around 1147 cm⁻¹ is attributed to PbSO₄(lead sulfate). Spectra show that ligand-exchanged QDs precipitated ininert conditions do not show this feature; methanol wash introduces someoxidation; ligand-exchanged QDs precipitated under an air ambient showevidence of strong oxidation. These results agree with the XPS dataabove.

Some performance characteristics of various representative deviceshaving different kinds of QD nanocrystal layers (e.g.,neck-then-oxidize, oxidize-then-neck, butylamine-capped, andneck-then-overoxidize) were measured. The general device structure isgenerally similar to that of FIG. 7 e. The device included a transparentglass substrate; two gold electrodes having a length of about 3 μm, awidth of about 5 μm, and being spaced from each other by about 5 μm; anda QD nanocrystal of variable thickness between the electrodes.

Photoconduction was studied with the aid of optical excitation throughthe glass substrate, with excitation radiation 1000 being transmittedthrough the space separating interdigitated electrodes, i.e., where theQD layer was formed. The current-voltage characteristics for twodifferent QD nanocrystal layer thickness were acquired, specifically theI-V characteristic for a “thin” 100 nm and a “thick” 500 nm QDnanocrystal layer devices. Photocurrents and dark currents respondlinearly to applied bias. The responsivity of the thick device reached166 A/W. The linear I-V characteristic indicates an ohmicelectrode-nanocrystal contact and suggests not a tunneling but a strong,direct conductive connection between QD nanocrystals. Photocurrent inthe thick device is significantly higher than the photocurrent of thethin device by virtue of greater absorbance in the thick device.

In order to determine optical power incident over the detector area andto calculate the responsivity R, a 2 mm radius beam from a 975 nm laserwas incident, first through a series of optical attenuators of knowntransmittance, and thence through the glass substrate, onto the devicefrom the back side. On the top surface, infrared-opaque interdigitatedgold electrodes were separated by 5 μm over a 3 mm path length. Theoptical power incident on the device was obtained by integrating theintensity profile of the laser over the unobstructed area of the device.Current-voltage characteristics were acquired using an Agilent 4155semiconductor parameter analyzer. The optical power impinging on eachdevice was about 80 pW.

The responsivity as a function of applied bias of devices made withdifferent kinds of QD nanocrystal layers was acquired. Here, thenanocrystal layers were about 800 nm thick. The “neck-then-oxidize” QDdevice, corresponding to a device having a layer of fused QDs withdefect states on their outer surfaces, can clearly be seen to have asignificantly higher responsivity than the other devices. The“oxidize-then-neck” QD device, in which the ligands are removed from theQDs, and the QDs are fused, but in which the QDs are not maintained inan inert atmosphere between the steps of ligand removal and QD fusing,has defect states in the regions in which the QDs are joined thatreduces their responsivity, as compared with the “neck-then-oxidize”device, in which the QDs are maintained in an inert atmosphere betweenthe steps of ligand removal and QD fusing. All of the “necked” deviceshave a significantly higher responsivity than the device havingbutylamine capped QDs, in which the butylamine ligands block facileconduction of electrons between QDs.

In general, the responsivity of QD devices (particularly the “neck thenoxidize” QD devices) as measured in A/W is at least about 10 A/W, 100A/W, 1000 A/W, or even more than about 10000 A/W. The responsivity is afunction in part of the bias voltage applied, with a greaterresponsivity at higher bias. In some embodiments, the QD devices(particularly the “neck then oxidize” QD devices provide a substantiallylinear responsivity over 0-10 V with a bias applied across a distance of0.2 to 2 μm width or gap.

With respect to responsivity, “necked” devices have a significantlyhigher dark current density than the device having butylamine cappedQDs. Devices made using QDs exposed to oxygen before necking(“oxidize-then-neck”) show a superlinear I-V behavior characteristic offield-assisted transport. In contrast, devices made using QDs fusedbefore oxidation (“neck-then-oxidize”) exhibit linear(field-independent) behavior. Further oxidation of neck-then-oxidizedevices (“neck-then-overoxidize) leads to a decrease of conductivityowing to excessive oxide formation.

Noise current was measured as a function of the measured dark currentfor the devices described. “Neck-then-oxidize” devices exhibited thelowest noise current, approaching within 3 dB the shot noise limit.“Oxidize-then-neck” devices had the highest noise current, consistentwith multiplicative noise. “Neck-then-overoxidize” QD devices showedlower noise levels than the oxidize-then-neck QD devices although theycontained larger amounts of oxide. This indicates the role of theoxidation step in the fabrication process. The Johnson noise limit, theshot-noise limit, and the fundamental background-limited thermodynamic(BLIP) noise current of the best-performing device (neck-then-oxidize)are also plotted for comparison.

Normalized detectivity D* was acquired as a function of applied bias.The normalized detectivity D* is measured in units of Jones (cmHz^(1/2)W⁻¹). D* is given as (AΔf)^(1/2)R/I_(n), where A is the effective areaof the detector in cm², Δf is the electrical bandwidth in Hz, and R isthe responsivity in AW⁻¹ measured under the same conditions as the noisecurrent i_(n) in A. The material figure of merit D* allows comparisonamong devices of different powers and geometries. The device figure ofmerit, noise equivalent power (NEP)—the minimum impinging optical powerthat a detector can distinguish from noise—is related to D* byNEP=(AΔf)^(1/2)/D*. The normalized detectivity D* is the highest for the“neck-then-oxidize” device, and the lowest for the “oxidize-then-neck”device. In other words, allowing the QDs to be exposed to oxygen afterligand removal and before necking or fusing significantly affects thenormalized detectivity of the finished device. In the example devicesshown, the normalized detectivity of the “neck-then-oxidize” device ismore than an order of magnitude higher than that for the“oxidize-then-neck” device. The highest detectivity was found at amodulation frequency of 30 Hz, and reached 1.3×10¹³ jones at 975 nmexcitation wavelength. In embodiments, detectivity may reach 1.3×10¹⁴jones.

The spectra of responsivity and the normalized detectivity D* wereobtained for the “neck-then-oxidize” device at an applied bias of 40 Vand an electrical frequency of 10 Hz. D* was measured to be 1.8×10¹³jones at the excitonic peak wavelength. The 3-dB bandwidth of thedetector is about ˜18 Hz, consistent with the longest excited-statecarrier lifetime in the device. High sensitivity (D*>10¹³ jones) isretained at imaging rates of about 30 frames per second.

The photocurrent temporal response following excitation of the QD layerof the “neck-then-oxidize” was obtained, where the excitation was a 7 nspulse centered at 1064 nm, at a frequency of 15 Hz. This allowsinvestigation of the transit time and distribution of carrier lifetimesin the device. The response of the detector to the optical pulse wasfound to persist over tens of milliseconds, attributable to thelongest-lived population of trap states introduced by oxidation. Theresponse exhibits multiple lifetime components that extend frommicroseconds (though shorter components may exist they are notobservable in this measurement) to several milliseconds. Decaycomponents were found at about 20 μs, about 200 μs, about 2 ms, about 7ms, and about 70 ms. A transit time of about 500 ns was obtained for abias of about 100 V, revealing that transit time depends linearly onbias with a slope corresponding to a mobility of about 0.1 cm²V⁻¹s⁻¹.The ratio of the longest component of carrier lifetime to the transittime was thus on the order of about 10,000. The observed responsivity ofabout 2700 A/W in this example could thus be explained byphotoconductive photovoltaic gain, given the films absorbance of 0.3 atan optical wavelength of 975 nm. This high responsivity was observedunder low-level optical power conditions relevant to ultrasensitivedetection. In general, in some embodiments, as illumination intensitywas increased, the longest-lived trap states became filled, and shorterlived, so lower-gain trap states began to account for a significantcomponent of carrier lifetime. The devices of these embodiments werethus highly sensitive under low-radiation 1000 conditions, and exhibitintrinsic dynamic-range-enhancing gain compression under increasingillumination intensity.

For determining the photocurrent spectral response, a bias of 50 V wasapplied to the sample connected in series with a 100 Ohm load resistor.Illumination was provided by a white light source dispersed by a Triax320 monochromator and mechanically chopped at a frequency of ˜100 Hz.Filters were used to prevent overtones of the monochromator's gratingfrom illuminating the sample. The voltage across the load resistor wasmeasured using a Stanford Research Systems SR830 lock-in amplifier. Theintensity through the monochromator at each wavelength was measuredseparately using a calibrated Ge photodetector. The photocurrent at eachwavelength was subsequently scaled accordingly. After the photocurrentspectral shape was determined in this way, the absolute responsivity at975 nm was used to obtain the absolute spectral response 800 nm-1600 nm.

For measurement of noise current and calculation of NEP and D*, thephotoconductive photovoltaic device was placed inside anelectrically-shielded and optically-sealed probe station and connectedin series with a Stanford Research SR830 lock-in amplifier. Alkalinebatteries were used to bias the device for the measurement of the noisecurrent in order to minimize noise components from the source. Thelock-in amplifier measured the current in the photodetector and reportednoise current in A/Hz^(1/2). Special care was taken in choosing anappropriate passband in order to acquire stable and meaningfulmeasurements of noise current at various frequencies. This measurementrevealed a significant increase in the noise current below 5 Hz which isattributed to 1/f noise, while white noise patterns are observed above50 Hz. The noise current divided by the responsivity under the samemeasurement conditions of applied bias and frequency modulation yieldedthe noise equivalent power (NEP). The normalized detectivity, D*, wasobtained as a function of wavelength, applied bias, and frequency bydividing the square root of the optically active area of the device bythe NEP.

To validate the NEP values obtained using this technique, the identicalprocedure was preformed using a commercial Si detector with known NEP.The system described above reported NEP values of the same order ofmagnitude, but typically somewhat larger than, the specified NEPs. TheNEP and D* determination procedure used herein thus provides aconservative estimate of these figures of merit.

Spectral dependence of responsivity and normalized detectivity D* wereobtained for biases of 30, 50, and 100 V, under 5 Hz optical modulationand 0.25 nW incident optical power. The responsivity shows a localmaximum near 1200 nm corresponding with the exciton absorption peak ofthe nanocrystal solid-state films. The responsivity increases withvoltage (but not as rapidly as does the noise current, resulting inhigher D* at lower biases) and reaches 180 A/W at 800 nm. For 30 and 50V of applied bias, D* is 2×10¹¹ Jones and is more than double thedetectivity of commercial polycrystalline PbS detectors which havebenefited from 50 years of science and technology development. Thoughthe responsivity is higher at 100 V, the bias-dependence of the measurednoise current results in D* being maximized at the lower bias of 30 V.In embodiments, processing steps may produce detectivity orders ofmagnitude greater, such as 10¹³ Jones, or even 10¹⁴ Jones.

The frequency dependence of responsivity and normalized detectivity wereacquired for three values of applied bias at 975 nm and 0.25 nW ofincident optical power. The 3 dB bandwidth of the device responsivitywas 15 Hz for 100 V and 50 V and 12 Hz for 30 V. The measurements weretaken with optical excitation from a 975 nm laser and incident opticalpower 0.2 nW. The noise current was also measured for the threedifferent biases throughout the frequency range. The noise current wassignificantly higher at frequencies below 20 Hz, whilefrequency-independent white noise was observed at higher frequencies.Noise equivalent exposure, or NEE, is another way of expressing thelowest amount of radiation 1000 detectable by a detector. NEE is definedto be the number of joules of optical energy that can create a signal atthe detector that is equivalent in magnitude to the noise on thedetector, and is calculated to be the RMS noise on the detector, dividedby the responsivity of the detector. FIG. 6 c shows the NEE of a QDdevice having a layer of fused QDs with defect states (e.g., oxidation)on their outer surface, as compared with the NEE of a conventional SiCCD detector as well as a conventional Si CMOS detector. The QD devicehas an NEE of less than 10⁻¹¹ J/cm² at wavelengths of 400 to 800 nm, andfurther less than 10⁻¹⁰ J/cm² at wavelengths of 400 to 1400 nm. The NEEsof the conventional Si devices are significantly higher than that of theQD device, in some cases more than an order of magnitude higher. Again,in embodiments, processing steps may produce detectivity orders ofmagnitude greater, such as 10¹³ Jones, or even 10¹⁴ Jones.

The figures of merit obtained from the quantum dot detectors presentedherein result from a combination of processing procedures. First, theshortening of the distance between QDs via exchange to a much shorterorganic ligand provided enhanced inter-QD conduction. Post-depositiontreatment using a nonsolvent and exposure to elevated temperatures in anoxygen-rich atmosphere enabled further ligand removal, QD fusing, andthe formation of a native oxide on the QD surface. This oxide haspreviously been shown in polycrystalline PbS devices to be useful inachieving high D* in photoconductors. However, chemical bath-grownpolycrystalline devices with 200 nm domain sizes do not allow refinedcontrol over interfaces. In contrast, using pre-fabricated, highlymonodisperse, individually single-crystal QDs with highly-controlledligand-passivated surfaces to fabricate optical devices allowsexceptional control over interface effects compared withpolycrystalline-based devices. The quantum dot optical devices describedherein are superior across many figures of merit to conventionalgrown-crystal semiconductor optical devices. At the same time thefabrication of the devices is strikingly simple, while maintainingoptical customizability based on the quantum size effects of quantumdots.

When QDs are fabricated they typically include a plurality of relativelylong ligands attached to their outer surfaces.

Then, the QDs are ligand-exchanged e.g. by substituting shorter ligandsfor those used during fabrication of the QDs. This step may allow theQDs to pack more closely in subsequent processing steps.

Then, the QDs are deposited on a suitable substrate), e.g., on anelectronic read-out integrated circuit. This step may be accomplishedwith various solution-based methods, many of which are compatible withstandard CMOS processes such as spin-coating.

Then, the precursor layer is washed to remove the ligands on the QDs,and to cause necking (i.e. touching) between at least some adjacentQDs).

Then, the necked QD layer is annealed, which fuses necked QDs together.

Then, defect states are created in the fused QD layer, e.g., byoxidizing the layer.

In general, when fabricating a device intended to have multiple pixels,the QD layer may then optionally be patterned, e.g., usingphotolithography, to separate the continuous layer into a plurality ofpixels.

The resulting QD layer can be incorporated into devices such as thosedescribed herein.

Activation of the film may proceed with a methanol dip, however, thismay associated with cracking of the film. An air bake of the film mayactivate the film without cracking. The air bake may operate withambient air. There may be no need for special gas treatment, such as andwithout limitation, a nitrogen purge. Anhydrously prepared quantum dotmaterials 200 may activate with an air bake, but not with methanol.Hydrous quantum dot materials 200, such as those stored in chloroform,may not activate with an air bake, but they may activate with methanol.The baking temperature may vary, such as within a range from about 90degrees Celsius to 130 degrees Celsius. The baking time may vary, suchas within a range from 60 to 180 minutes.

In an embodiment, a post-film formation treatment may involve a methanoldip. The methanol dip may occur in ambient air. The methanol dip mayoccur at room temperature. Activation may not be optimal in an anhydrousenvironment with anhydrous drying, however, doing the methanol dip in anenvironment such as that of a glove box and then evaporating themethanol in room air may activate the film. Methanol dip may involveactivation after removal of ligand. After methanol dip, the device maybe brought out to air for controlled exposure. The mechanism by whichthe oven operates may not be limiting for this embodiment. In anembodiment, the butyl amines are removed first and then the film isoxidized. Alternatively, the film may be oxidized first, and then thebutyl amines are removed.

In an embodiment, the quantum dot materials may be patterned. Patterningmay involve forming a non-homogeneous layer. Patterning may involvecarving out rows and columns that are electrically independent.Patterning may involve enabling passivation of a portion or portions ofthe film. Patterning may enable a self-assembly quantum dot pixel 1800.Patterning may enable a self-isolated quantum dot pixel 1800. Patterningmay be used on a coarse scale. Patterning may involve patterning thesubstrate. Patterning of the substrate may contribute, in part, topatterning of a film disposed on the substrate. Patterning may assist inchoosing a bias level to obtain a desired sensitivity of the QPDC 100.Patterning may provide feedback on deviations as multiple layers areformed. There may be multiple techniques for patterning, including dryetching, chlorine or fluorine etching of sulfides, and maskingPatterning may involve self-assembly. Crosslinkers may enable selfassembly of patterns, such as ligand exchange in real time.Bi-functional linkers may facilitate self-assembly of patterns. One endof a bi-functional linker may be attached to the substrate and anotherto the quantum dot 1200. Bi-functional linkers may be designed tosequentially link quantum dots 1200 to substrate, and then quantum dots1200 to quantum dots 1200.

Methods of producing optically sensitive layers, including thosepatterned to form regions of material, are now discussed. Methods ofgrowth for self assembly of pattern may involve methods analogous toepitaxial growth, but where the atomic or molecular species employed inepitaxy are replaced in the analogy with the quantum dots. Growth mayinvolve a nucleation point which leads to a large single crystal, suchas single crystal formation, or polycrystalline-type growth. The growthmethod may depend on how the linker attaches to the substrate. A patternthat begins with a single monolayer may continue as subsequentmonolayers are deposited on the substrate, similar to epitaxial growth.There may be ranges for epitaxial growth. For example, only where thereare atoms of the right kind of crystal will growth occur. There may bethree modes for selective area epitaxy. One mode may be molecular beamepitaxy (MBE). With MBE, there may be good crystal on crystal growth.The thickness of what grows on crystal is what would have grown with nomask. With MBE, materials for growth may adhere anywhere along asubstrate. Another mode may be metalorganic chemical vapor deposition(MOCVD). With MOCVD, growth only occurs on regions of crystal, butgrowth proceeds with a large effective width. With MOCVD, precursorsdeposited on a substrate may move around, crack, and adhere randomly.Another mode may be chemical beam epitaxy (CBE). With CBE, growth tendsto occur only in the hole and may nominally be the same as if grown on aplanar surface. With CBE, precursors deposited on a substrate may bounceoff or, if at right place, crack and form a crystal. CBE may combine thebest of MBE and MOCVD. It may be possible to combine a quantum dot 1200with a delivery agent, such as a biomolecule. The combination of the twomay approach the surface of the substrate. Attached to the substrate mayreside a molecule that catalytically cleaves the bond between thebiomolecule (carrier) and the quantum dot 1200 (payload). The quantumdot 1200 may then be released at the point of attachment to thesubstrate. The quantum dot 1200 may be fastened to the substrate throughany of the means discussed herein, such as by linkers, self-aggregation,and the like.

For quantum dot 1200 precursors, growth may occur by any of theaforementioned techniques in varying environments, such as liquid,vacuum, and the like. For example, quantum dots 1200 may be provided,the excess may be disposed of, and the quantum dot 1200 may bemaintained in place on the substrate. No transport cracking process maybe needed. Quantum dot materials 200 may be locally activated.Activation may render the quantum dot materials sticky or reactive. Thequantum dot materials 200 may be fed some non-solvent. Quantum dots 1200may irreversibly activate after being centrifuged. Methanol may beapplied locally at the surface that may cause quantum dots 1200 toprecipitate down to the surface. A goal may be to deposit quantum dotmaterials 200 on the surface of a substrate. The system of ligandscapping the nanoparticle may be designed such that, in the solutionphase, far from the substrate, the nanoparticles remain dispersed.However, this same system of ligands may be designed such that, when thenanoparticle approaches the substrate, the nanoparticle's environmentbecomes asymmetric. This asymmetry may break the ligand cage surroundingthe quantum dots 1200 and may result in aggregation of the quantum dots1200 near to or onto the substrate.

In an embodiment, quantum dots 1200 may be post-processed. Postprocessing may involve precipitation and redispersion. Post-processingmay be anhydrous. Post-processing may involve drying the quantum dots1200, resuspending them in a solvent, filtering the solution,concentrating the solution, then spinning the solution. This method maybe an improvement over simply evaporating the solvent by blowing off thesolvent in an air stream which may generate quantum dots 1200 but mayalso cause splashes which may result in droplets. An improvement innitrogen evaporation may comprise maintaining an enriched nitrogenenvironment. Another improvement may involve, when going from above,injecting nitrogen in to a drying chamber through a high velocity ventwith little entrainment of air. This improvement may result in a morestable surface that may not splash to form droplets. Another improvementmay be to the drying chamber itself, such as applying a vacuum to achamber, such as a glove box, maintaining a pressure differentialbetween two needles in the chamber, and providing a pump with seals thatmay be operable with chloroform and able to pump in a nitrogen flow andpump out vapor through a fume hood. Redispersion may be soaking theprecipitated quantum dots 1200 in a solvent, such as butyl amine,toluene, and the like to provide for ligand exchange. Non-toluene soaksmay provide faster redispersion. The quantum dots 1200 may need tomature for a time period, such as in the range of five days.

In an embodiment, quantum dot materials 200 may be encapsulated. A filmof quantum dots 1200 may be spin coated to a particular thickness on aprocessed wafer with electrodes at its planar surface. The surface ofthe wafer may be substantially planar. The film may be patterned toremove areas of wire bonds and electronics. Materials to which wirebonding is conventionally done include Al and Al capped ti TiN or TaN.Patterning may involve coating the film with a material which may or maynot be an encapsulant. This material may be a mechanical and/or chemicalbuffer between quantum dots 1200. Then, photoresist may be put overthis, such as with a dry etch, to take off the encapsulant or interfacelayer plus the quantum dots that are underneath it. Then, thephotoresist may be removed or left behind. The etch rate of photoresistremoval may be comparable on a thickness adjusted basis so it may begone anyway. This process may provide an island of quantum dots 1200 inthe middle of a chip. There may be material on top of this island ofquantum dots 1200 that may remain in place. The island of quantum dots1200 may be reencapsulated. The reencapsulant may be a hermeticmaterial. The reencapsulant may touch the chip and travel up the sidesof the island of quantum dots 1200 to encapsulate it fully.Reencapsulant around the outside that touches the wafer may be removed.If there are bond pads, holes may be opened only where needed.Alternatively, the bond pads may be processed.

In an embodiment, quantum dot materials 200 may include quantum dots1200, as described herein. Quantum dot materials 200 may also includehard dielectrics, such as and without limitation, nitrides and oxidesmay be used. For example, graded transitions from nitrides to oxideswith oxynitrides in between may be used. Certain parameters may bevariable for the film, such as and without limitation, stress, grading,chemistry of the initial surface, chemistry of the final surface, therelationship to bond pads, and the like.

In an embodiment, quantum dot materials 200 may comprise a topology. Thequantum dot materials 200 may be completely surrounded by material thatmay be impermeable to oxygen, such as for example, encapsulated siliconchips. In a topology, oxides may be followed by nitrides or vice versa.In an embodiment, nitrides may be placed close to quantum dots 1200. Aslong as the stress level on the first film is not exceeded, there may bevariations in the order and thickness of the nitride and oxide. Thefinal layer of quantum dot materials 200 should look like the finallayer of a regularly processed chip going through the same foundry tomaintain compatible chemistry. For example, the topology may start withnitride, oxide may be added, and then the layers may be finished off.The topological characteristics may include a chemistry for the bottomlayer, stress management for the middle layer, and chemistrycompatibility for the final layer.

In embodiments, colloidal quantum dots capped with organic ligands areprocessed in the solution phase in order to introduce a new organicligand, or combination of ligands. For example, colloidal quantum dotsmay be introduced into a solution containing a mixture of shorter thiols(such as ethanethiol, butanethiol, or hexanethiol) and longer thiols(such as hexanethiol, octanethiol, or dodecanethiol). In embodiments,the solvent employed may be chloroform. In embodiments, the ratio ofshort to long thiols may be 6:1 or 7:1. In embodiments, the short thiolmay be chosen to be hexanethiol and the longer thiol chosen to bedodecanethiol. In embodiments, the ratio of short to long thiols may be3:1. In embodiments, the short thiol may be chosen to be ethanethiol andthe longer thiol chosen to be hexanethiol.

In embodiments, a photoconductive film is implemented with the followingproperties: (1) A dark current density of less than 100 nA/cm2 underrelevant electrical bias; (2) A photoconductive gain of between 1 and20, with good values including 2, 3, 5, 10, and 15; (3) A singlecomponent to the temporal rise time and fall time that lies between 1millisecond and 100 milliseconds, with 1, 2, 5, 10, 30, 50, 70, and 100milliseconds being good values.

In embodiments, a photoconductive film is constituted from materialsthat, when combined to form the film, possess, for at least one carriertype (such as electrons), a substantially pure trap state, resultantfrom a substantially pure chemical species, that produces in thephotoconductive film a temporal rise time and fall time that liesbetween 1 millisecond and 100 milliseconds, with 1, 2, 5, 10, 30, 50,70, and 100 milliseconds being good values.

In embodiments, a photoconductive film consists of colloidal quantumdots, of substantially the same diameter, made principally of asemiconductor such as PbS (lead sulfide), having one or more ligands orlinker molecules, and having a substantially single impurity, leadsulfite (PbSO3), substantially localized to its surface, that has atroom temperature a substantially single time constant of about 25-35milliseconds.

In embodiments, a photoconductive film consists of a semiconductor suchas PbS that is decorated with substantially only one single class ofimpurity species, such as lead sulfite (PbSO3), and is substantiallylacking in other impurities, such as Pb-carboxylate, lead sulfate(PbSO4), lead oxide (PbO).

In embodiments, a first film is proximate to the electrical contacts andserves to make an ohmic contact, or a low-barrier-voltage nonohmiccontact; and is followed by a second film atop this first film thatserves as the photoconductive layer.

In embodiments, a first film is proximate to the electrical contacts andserves to block the egress of one carrier type, such as electrons, whilepermitting the egress of the other carrier type, such as holes; and isfollowed by a second film atop this first film that serves as thephotoconductive layer.

In embodiments, a photoconductive phototransistor is formed laterallyatop an array of electrical contacts. A first film, having a largerbandgap, and being more strongly p-doped, is proximate to the contacts.This film may not extend continuously between the contacts, but mayinstead simply cover each contact and not span the space in between. Asecond film, having a smaller bandgap, and being n-type, ornear-intrinsic, or more mildly p-type, resides atop the first (possiblynon-continuous) film.

Embodiments include an array of photoconductive photodetectors whereincertain spatial regions of the array have a heightened sensitivity tocertain bands of wavelengths, and a much lower sensitivity to otherbands of wavelengths. For example, certain spatial regions may have aheightened sensitivity to blue colors compared to red, green,ultraviolet, and infrared. Embodiments include an array wherein saidcolor sensitivity is achieved by combining photoconductive materialswith wavelength-selective-optically-absorbing materials such as thoseused to form a color filter array.

Embodiments include pixels wherein two components—one a photoconductivematerial, the other a wavelength-selective-light-absorbingmaterial—substantially phase-segregate in the course of processing,resulting in the top portion of the pixel being constituted principallyof the wavelength-selective-optically-absorbing material, and the bottomportion of the pixel being constituted principally of thephotoconductive material.

Means of producing optically sensitive layers, and of integrating themon a substrate, are now discussed. In an embodiment, puddle casting maybe used to deposit quantum dot materials 1200 on a photodetectorstructure 1400. Puddle casting may comprise depositing a metered amountof quantum dot materials 200 onto a substrate and allowing solution toevaporate. The resultant films may or may not crack. Puddle casting mayenable deposition of a certain number of quantum dots 1200 per planarsquare centimeter on a non-planar surface. Puddle casting may enable aconformal coating over photodetector structures 1400 without spincoating. Puddle casting may be similar to electrodeposition ormetalorganic chemical vapour deposition (MOCVD) in that puddle castingmay result in concentration grading or changes in concentration overtime, rather than just a pattern. Puddle casting may proceed withmaterials that may undergo a phase change. A goal of puddle casting maybe to set the inter-quantum dot 1200 spacing appropriately with speciesthat may be managed appropriately in film form. A goal of puddle castingmay be to appropriately distribute the quantum dots 1200 in an operableconfiguration and/or a user-defined way. A goal of puddle casting may beto obtain a spatially uniform film with desired dark conductivity,desired photoconductive photovoltaic gain, desired noise current, andthe like. A goal of puddle casting may be to set the stage withdeposition for later actions.

In an embodiment, quantum dot materials 200 for puddle casting maycomprise a quantum dot 1200 in solvent or solvents. The solvents may beof varying degrees of volatility. For example, the solvent may be acombination of a high volatility solvent, such as n-hexane, with a lowvolatility solvent, such as octane. The solvent may be a “less” solvent,such as 2-propanol. The solvent may be a “good” solvent, such as tolueneor chloroform. Quantum dot materials 200 may also comprise ligands.Ligands may be used to passivate the quantum dots 1200, such as butylamine, benzenethiol, benzenedithiol, octylamine, pyridine. Quantum dotmaterials 200 may also comprise non-solvents. Non-solvents, such asmethanol, ethyl acetate, acetonitrile, propanol, and iso-propanol, maycause precipitation and film formation. Quantum dot materials may alsocomprise cross-linkers, such as acetonitrile (MeCN), ethanethiol (ET),ethanedithiol (EDT) or benzenedithiol (BDT). The parameters that may beimportant in puddle casting film formation may be introduction ofmaterials in the gas phase, temperature, pressure, and time. Puddlecasting may enable obtaining a dense film with high mobility. Puddlecasting may enable obtaining a smooth, uniform, uncracked film. Ligandexchange during film formation may be possible, as described herein.Ligand exchange may proceed at substantially the same time as filmformation to obtain a high density, uniform film. Also as describedherein, ligand exchange during film formation may also apply to filmformation by growth from solution and ink jet printing. For example, ingrowth from solution, the wafer sample may be submerged in a quantum dotsolution 400 and quantum dots 1200 in solution may self-deposit oraggregate on the wafer in response to an affinity for already depositedquantum dots 1200 or in response to chemical manipulation by across-linker, such as ligand exchange, or a non-solvent. Temperature maybe a factor in the precipitation of the material onto the substrate.Crosslinkers or non-solvents may also be introduced into the quantum dotsolution 400 or deposited as a layer on the wafer or substrate. It maybe possible to have stable colloid solutions and have the process ofdeposition occurring accompanied by ligand exchange/cross-linkers. Inany event, as volatile solvent evaporates from the puddle, highlyconcentrated quantum dots 1200 are left deposited on the substrate. Afactor in puddle casting may be puddle confinement.

After forming the QD precursor layer, the QDs may be fused together toproduce a QD film with enhanced optical and electrical characteristics,and which is suitable for use in a finished electronic or optoelectronicdevice.

In one embodiment, at least a portion of the QDs in the QD precursorlayer are fused by annealing the layer at temperatures up to about 450°C., or between about 150° C. and 450° C. In other embodiments, the layeris treated at lower temperatures, for example between about roomtemperature up to about 150° C., or up to about 100° C., or up to about80° C. In some embodiments, the QD precursor layer is not heatedsubstantially above ambient (room) temperature. As mentioned above, thestep of fusing brings the cores of adjacent QDs into direct physical andelectrical contact. It is also possible to “overfuse” the QDs, in whichcase they may lose their individual characteristics and appear more likea bulk semiconductor material. It is desirable to prevent suchoverfusing through the parameters chosen for annealing or throughmonitoring to prevent an overfused condition. The annealing step willtypically be performed in a vacuum or in an otherwise anhydrousenvironment to prevent the development of defect states (e.g.,oxidation) on the outer surfaces of the QDs before the cores of the QDsfuse together. This way, there will be substantially no defect states inthe regions where the QDs are joined together, but these regions insteadwill have a substantially homogeneous composition and crystallinestructure. In other embodiments the fusing step may be performed in anoxygen-rich environment, or an oxygen environment in which the partialpressure of oxygen is regulated.

The ligands in the QD precursor layer are also typically removed, eitherbefore or concurrently with the fusing step. For example, if the ligandsin the QD precursor layer are volatile, they may easily be removedduring annealing because they will simply volatilize from the heat. Or,for example, if the ligands in the QD precursor layer are not volatile,they can be removed from the QD precursor layer by soaking the layer ina solvent that dissolves and thus dissociates the ligands from the QDsbut which does not generally disrupt the arrangement of QDs in the QDlayer. In general, it is preferable that removing the ligands does notsignificantly change the volume of the QD layer, e.g., by less thanabout 30%; a large volume change may crack or otherwise damage thefinished QD film.

In many embodiments, particularly those suitable for opticalapplications, defect states are created on the outer surfaces of thefused QDs. By “defect state” it is meant a disruption in the otherwisesubstantially homogeneous crystal structure of the QD, for example, thepresence of a dislocation or a foreign atom in the crystal lattice. Inmany cases this defect state will exist on the outer surface of the QDs.A defect state can be created by, e.g., oxidizing the QDs after fusingand ligand removal. During operation, if an electron-hole pair isgenerated within the QD film, one or more holes may be trapped by thedefect state; this will preclude rapid recombination of holes withelectrons, which will then allow the electrons to flow for a much longertime through the film. This can positively affect photoconductivephotovoltaic gain, among other things.

In general, the outer surface of the fused QDs can be coated orotherwise treated so it has a different composition than the cores ofthe fused QDs. For example, the outer surface can include asemiconductor or insulator shell.

In embodiments, colloidal quantum dots capped with organic ligands areprocessed in the solution phase in order to introduce a new organicligand, or combination of ligands. For example, colloidal quantum dotsmay be introduced into a solution containing a mixture of shorter thiols(such as ethanethiol, butanethiol, or hexanethiol) and longer thiols(such as hexanethiol, octanethiol, or dodecanethiol). In embodiments,the solvent employed may be chloroform. In embodiments, the ratio ofshort to long thiols may be 6:1 or 7:1. In embodiments, the short thiolmay be chosen to be hexanethiol and the longer thiol chosen to bedodecanethiol. In embodiments, the ratio of short to long thiols may be3:1. In embodiments, the short thiol may be chosen to be ethanethiol andthe longer thiol chosen to be hexanethiol.

In embodiments, a photoconductive film is implemented with the followingproperties: (1) A dark current density of less than 100 nA/cm2 underrelevant electrical bias; (2) A photoconductive gain of between 1 and20, with good values including 2, 3, 5, 10, and 15; (3) A singlecomponent to the temporal rise time and fall time that lies between 1millisecond and 100 milliseconds, with 1, 2, 5, 10, 30, 50, 70, and 100milliseconds being good values.

In embodiments, a photoconductive film is constituted from materialsthat, when combined to form the film, possess, for at least one carriertype (such as electrons), a substantially pure trap state, resultantfrom a substantially pure chemical species, that produces in thephotoconductive film a temporal rise time and fall time that liesbetween 1 millisecond and 100 milliseconds, with 1, 2, 5, 10, 30, 50,70, and 100 milliseconds being good values.

In embodiments, a photoconductive film consists of colloidal quantumdots, of substantially the same diameter, made principally of asemiconductor such as PbS (lead sulfide), having one or more ligands orlinker molecules, and having a substantially single impurity, leadsulfite (PbSO3), substantially localized to its surface, that has atroom temperature a substantially single time constant of about 25-35milliseconds.

In embodiments, a photoconductive film consists of a semiconductor suchas PbS that is decorated with substantially only one single class ofimpurity species, such as lead sulfite (PbSO3), and is substantiallylacking in other impurities, such as Pb-carboxylate, lead sulfate(PbSO4), lead oxide (PbO).

In embodiments, a first film is proximate to the electrical contacts andserves to make an ohmic contact, or a low-barrier-voltage nonohmiccontact; and is followed by a second film atop this first film thatserves as the photoconductive layer.

In embodiments, a first film is proximate to the electrical contacts andserves to block the egress of one carrier type, such as electrons, whilepermitting the egress of the other carrier type, such as holes; and isfollowed by a second film atop this first film that serves as thephotoconductive layer.

In embodiments, a photoconductive phototransistor is formed laterallyatop an array of electrical contacts. A first film, having a largerbandgap, and being more strongly p-doped, is proximate to the contacts.This film may not extend continuously between the contacts, but mayinstead simply cover each contact and not span the space in between. Asecond film, having a smaller bandgap, and being n-type, ornear-intrinsic, or more mildly p-type, resides atop the first (possiblynon-continuous) film.

Embodiments include an array of photoconductive photodetectors whereincertain spatial regions of the array have a heightened sensitivity tocertain bands of wavelengths, and a much lower sensitivity to otherbands of wavelengths. For example, certain spatial regions may have aheightened sensitivity to blue colors compared to red, green,ultraviolet, and infrared. Embodiments include an array wherein saidcolor sensitivity is achieved by combining photoconductive materialswith wavelength-selective-optically-absorbing materials such as thoseused to form a color filter array.

Embodiments include pixels wherein two components—one a photoconductivematerial, the other a wavelength-selective-light-absorbingmaterial—substantially phase-segregate in the course of processing,resulting in the top portion of the pixel being constituted principallyof the wavelength-selective-optically-absorbing material, and the bottomportion of the pixel being constituted principally of thephotoconductive material.

Embodiments include sensitive, low-dark-current photodetectors based onfilms made using colloidal quantum dots. Embodiments include pixelswhose composition gives them desirable photoconductive photodetectorcharacteristics, including high sensitivity, where sensitivity impliesability to detect low light, and high signal-to-noise ratio. Otherdesirable characteristics of the pixels include speed, or low lag, whichallows photos or videos to be captured without ghosting effects. Thepixels described are also very responsive. Responsiveness is related tosensitivity, but is not the same thing. As used herein, responsivenessimplies a relatively large amount of electrical signal for a givenamount of optical signal. The pixels described further achieve a lowbackground level. The pixels described are readily integrated with acompleted or partially-completed electronic integrated circuit thatachieves low-noise read-out of a signal that is related, in a known way,to the integrated photon flux received during a specific integrationperiod, and that conveys the resultant electronic signal to otherportions of the integrated circuit such as amplifiers, analog-to-digitalconverts, digital logic processing, and memory.

Embodiments of photoconductive photodetectors including the pixelsdescribed herein retain high levels of signal-to-noise at low lightlevels.

Embodiments of photoconductive photodetectors including the pixelsdescribed herein also reduce by many orders of magnitude the amount ofcurrent flowing in these devices when they are in the dark (the darkcurrent), thereby dramatically improving the signal-to-background ratiofor a given level of illumination.

Embodiments of photoconductive photodetectors including the pixelsdescribed herein also ensure that the device exhibits response to light,and recovery from light, that is sufficiently fast to allow blur-freeimaging with brief exposures (millisecond to second) and the capture ofsatisfactory video (e.g. 60 fps, 30 fps, 15 fps).

Embodiments including material compositions and method of manufacturedescribed herein are applicable to the previously describedarchitectures. In general, the device architectures include electrodesthat make an ohmic contact with a photoconductive material. This forms asimple circuit, for example a variable resistor when operated atconstant voltage. In this example, there is a current through thevariable resistor in the presence of light. The conductivity of thematerial ultimately determines the resistance, and is proportional tothe mobility and the carrier density. The mobility, or ease of carrierflow, and the carrier density describes the number of carriers that areavailable. The fact that these two numbers are non-zero means even inthe dark there is some density of charge carriers (electrons, holes, orboth) that will flow and create a background. Upon illumination, thereis an increase in conductivity; presumably the propensity of thecarriers to flow will be substantially unchanged but the number ofcarriers will be different and an “excess carrier density” will exist.Change in current in response to the change in light which isattributable to a change in carrier density is what is sought to besensed.

A challenge in this simple photoconductor in prior devices is that thesignal to background ratio is equal to the change in the conductivitydivided by the conductivity and these mobility numbers are canceled,yielding a constant. This leaves a ratio of the change in carrierdensity to the underlying dark carrier density. The fact of not havingsufficient signal to background in this architecture is related to thefact that there is a single type of carrier flow in this device. Inorder to overcome this, embodiments employ a novel photodetectorstructure based on creating a phototransistor that allows entry into anew regime of sensitivity. A phototransistor can be pictured as abipolar junction transistor, which involves three contacts, each one toan emitter, a base, and a collector. Instead of having an electricalbase, light is the source of the third “signal”. Light is the signalthat is amplified, similarly to the base signal in a bipolar junctiontransistor. More particularly, the electrical signal that is inducedfrom the absorption of light is amplified.

Embodiments include a novel phototransistor instantiated in a colloidalquantum dot film as the photoconductive layer. Further embodimentsinclude various choices of the contacts, and the method of making thedevice, and elements of the physical device architecture.

Embodiments of the phototransistor take advantage of the fact that thereare two types of carriers flowing, which provides opportunities toimprove the ratio of signal to background in this device. For example,embodiments include a device in which the dark current flows in responseto electrons, and in which the change in conductivity due to light flowsin response to the excess holes. The mobilities do not cancel each otheras before, rather there is a mobility ratio which can be manipulated.

Embodiment further include a photoconductive photodetector based oncolloidal quantum dots in which, in the dark, one carrier type (e.g.electrons), is in the majority. Under illumination, even low lightlevels (e.g. <10 nW/cm2), the other carrier type (e.g. holes), providesthe predominant contribution to current flow.

Embodiments further include a photoconductive photodetector, which is asensor for light which provides gain based on trapping of one carriertype (e.g. Electrons) combined with flow of the other type (e.g. Holes).

Embodiments further include a photoconductive photodetector, in whichholes are in the majority; and under illumination, electrons dominatecurrent flow.

Embodiment also include a photoconductive photodetector made usingN-type colloidal quantum dots. This is distinct from a photodiode, orphotovoltaic, which employs a combination of n-and p-type materials).

Conversely, embodiments can include a P-type semiconductor, and alow-work-function metal (work function shallower than 4.5 eV, includingAl, Mg, Ag, Ca, suitably-treated TiN, TaN).

Embodiments further include a topology comprising a film comprising anetwork of fused nanocrystals, the nanocrystals having a core and anouter surface, wherein the core of at least a portion of the fusednanocrystals is in direct physical contact and electrical communicationwith the core of at least one adjacent fused nanocrystal, and whereinthe film has substantially no defect states in the regions where thecores of the nanocrystals are fused.

Embodiments also include the foregoing topology with an N-typesemiconductor in which colloidal quantum dots make up the semiconductor.

Embodiments also include the foregoing topology with an N-typesemiconductor in which colloidal quantum dots make up the semiconductor,wherein there is an absence of P-type semiconductor material.

Embodiments further include deep-work-function-contacts, which aremetals having a work function deeper than 4.5 eV. Examples include Au,Pt, Pd, ITO, Cu, Ni, and suitably-modified TaN and TiN.

Embodiments further include deep-work-function-contacts in combinationwith the N-type semiconductor in which colloidal quantum dots make upthe semiconductor. The deep-work-function-contact is described asSchottky, wherein an n-type semiconductor is contacted by a metal whosework function aligns more closely to its valence band (for holes) thanto its conduction band (which conducts electrons). Schottky contactshave been made previously generally between semiconductors and metals(in contrast to such contacts to colloidal quantum dot films.)

Embodiments also include deep-work-function-contacts in combination withthe N-type semiconductor in further combination with the topologydescribed above.

Embodiments also include noble metal contacts in combination with then-type semiconductor based on colloidal quantum dots.

As described below, there are various methods of implementing thephototransistor concept as stated above. For example, the choice ofmetal-semiconductor interface provides an opportunity to control thetype of carrier that is flowing. Embodiments include a selective contactthat injects or extracts holes, but not electrons. This provides accessinto a regime of discrimination between carrier types.

In other embodiments, the interface may not be a purely simplemetal-semiconductor interface. The desired selectivity could come froman intervening layer as well as from metal choice. The intervening layercould be a semiconductor or an insulator. In addition, embodimentsinclude devices in which there are a number of properties that arecontrolled through the photoconductive layer. One of these properties isthe ratio of hole mobility to electron mobility in this medium. Anotherproperty is the equilibrium carrier density; essentially the net doping.For example, in a semiconductor, a net type can be achieved throughso-called compensation.

Another attribute of the photoconductive layer that is exploited toachieve sensitivity, and is also important in achieving low lag, is thecarrier lifetime. As further described below, photoconductive layermaterials and the colloidal quantum dots that make up this material aredesigned to achieve the desired characteristics of the phototransistor.FIG. 39 is a block diagram of functional blocks of a lateral pixelaccording to an embodiment. FIG. 40 is a block diagram of functionalblocks of a vertical pixel according to an embodiment.

Aspects of various embodiments, including compositions of matter andmethods of making will now be described with reference to FIGS. 39 and40. While a wide variety of specific device geometries are possiblewithin the scope of the claimed invention, various devices typicallycomprise materials that possess one or more of the attributes describedbelow in various combinations. Referring the FIGS. 39 and 40, pixels 100and 200 each include an active layer (104 and 204, respectively),comprising a photoconductive material. Pixels 100 and 200 furtherinclude overlayers 102 and 202 that include passivation layers,encapsulation layers, transparent dielectrics, optical filters, otherpixels (active layers and contacts), and microlenses. Pixels 100 and 200further include injecting contacts 110 and 210 and withdrawing contacts108 and 208. Pixels 100 and 200 further include substrate layers 106 an206, including silicon CMOS integrated circuits. Active layers 104 and204 have one carrier type (e.g. holes) that is said to be the flowingcarrier. The flowing carrier typically has a mobility of 1E-5 cm2/Vs orgreater, with particularly desirable values including of 1E-4 cm2/Vs, of2E-4 cm2/Vs, and of 1E-3 cm2/Vs. The other carrier type in active layers104 and 204 (e.g. electrons), is said to be the trapped carrier.

In an embodiment, the trapped carrier possesses a mobility that is atleast 10× less than that of the flowing carrier type, with particularlydesirable values including 100× less than the flowing carrier and 1000×less than the flowing carrier. The trapped carrier further possesses acertain density of trap states having: lifetimes typically ranging from1 microsecond to 1 second, with particularly desirable values including1 millisecond, 6 milliseconds, 10 milliseconds, 30 milliseconds, and 50milliseconds; and densities ranging from 1E12 cm-3 to 1E22 cm-3, withparticularly desirable values including 1E14 cm-3, 1E15 cm-3, 1E16 cm-3,1E18 cm-3, and 1E19 cm-3. The flowing carrier travels through the devicewithout substantial addition of noise (such as multiplicative noise)beyond the shot noise and Johnson noise and generation-recombinationnoise proper to its operation as a resistor. If shot noise limits thedevice, then the number of noise electrons Q_n should not substantiallyexceed the square root of the number of dark electrons Q_d. If Johnsonnoise limits the device, then the noise current i_n should notsignificantly exceed Square Root (4 kB T Δf/R) where kB is Boltzmann'sconstant, T is the device temperature, Δf is the bandwidth, and R is thedevice's resistance.

In the absence of illumination, the volume-density of the flowingcarrier is extremely small. If holes are the flowing carrier, then thehole density may be 10^12 cm-3, making the active layer avery-lightly-doped p-type material. The hole density can be lower stillsuch as 10^6 cm-3, to make the active layer an effectively intrinsicmaterial. The hole density can be yet lower still such as 10^0 cm-3 orlower, rendering the active layer an n-type material. This ensures thatthe majority carrier is the trapped, instead of the flowing, carrier.

Pixels 100 and 200 each include an injecting contact (110 and 210) and awithdrawing contact (108 and 208). Under the biasing conditions, theinjecting contact injects the flowing carrier into the active layer withmuch greater efficiency than it withdraws the trapped carrier from theactive layer into the contact. Under the biasing conditions, thewithdrawing contact withdraws the flowing carrier from the active layerinto the contact with much greater efficiency than it injects thetrapped carrier into the active layer.

Biasing conditions include a bias on the injecting contact, relative tothe withdrawing contact, typically of +0.1 V, +1 V, +1.8 V, or +2.8 V,if the flowing carriers are holes. The polarity is opposite if theflowing carriers are electrons.

Pixels 100 and 200 each include an active layer of photoconductivematerial (104 and 204). In an embodiment the active layer materialconsists of mutually-touching semiconductor nanoparticles, where thenon-touching surfaces of the connected particles may be coated by one ormore of: an inorganic material such as an oxide or sulfate; and anorganic material such as an organic ligand.

The mutually-touching semiconductor nanoparticles may be made fromcrystalline semiconductors such as: PbS, PbSe, or PbTe; CdS, CdSe, orCdTe; Si, Ge, or C; In2Se3, In2S3, including either the alpha-phase orthe beta-phase; InP; and Bi2S3.

The inorganic material coating the non-touching surfaces of theconnected nanoparticles may include one or more of: PbSO4, PbO, PbSeO4,PbTeO4, and combinations thereof; SiOxNy in various proportions; In2O3in various proportions; sulfur, sulfates, and sulfoxides; carbon andcarbonates such as PbCO3; and metals or semimetals such as an excess ofPb, Cd, In.

The organic material coating the non-touching surfaces of the connectednanoparticles may include: Thiols such as ethanethiol, ethanedithiol,benzenethiol, benzenedithiol; Amines such as pyridine, butylamine, andoctylamine; Hydrazine; and Carboxylates such as oleic acid.

The dimension of the active layer perpendicular to the direction ofincident of light may typically be 100 to 3000 nm, with the thicknesschosen such that the wavelengths of light of interest are substantiallyabsorbed. For example, if PbS mutually-touching semiconductornanoparticles are employed, and if their volume fill fraction is greaterthan 10%, then a thickness of between 150 and 350 nm will typicallyachieve the substantial absorption of visible light.

Pixels 100 and 200 each include an injecting contact (110 and 210) and awithdrawing contact (108 and 208). The injecting contact and thewithdrawing contact are made using the same materials in embodiments, orare made using different materials from one another in otherembodiments. The contacts may consist of a conductive material such as ametal or a degenerately-doped semiconductor, or of a combination of suchmaterials.

If holes are the flowing carrier, the injecting contact may consist ofAu, Pt, Pd, Cu, Ni, NiS, TiN, TaN, or p-type polysilicon or p-typeamorphous silicon.

If electrons are the flowing carrier, the injecting contact may consistof Al, Ag, In, Mg, Ca, Li, Cu, Ni, NiS, TiN, TaN, or n-type polysiliconor n-type amorphous silicon.

The contacts may, in the alternative, consist of a combination of: ametal or a degenerately-doped semiconductor, or of a combination of suchmaterials; and a semiconductor or even an insulator, e.g., a materialhaving a bandgap. In the latter case, the second material (thesemiconductor or insulator) is typically the material in direct physicalcontact with the active layer. Examples of the first layer compositionare the same as listed above with reference to the contacts. Examples ofthe second layer (semiconductor or insulator) composition include a thin(e.g. 5-50 nm) layer of mutually-touching semiconductor nanoparticles,as described above in describing the active layer. However, in the caseof the second layer, this thin layer will typically be made using alarger-bandgap material (e.g. smaller nanoparticles of the samematerials composition as the active layer, or different nanoparticleshaving a larger bandgap than the active layer and also potentially adifferent size). In addition, this thin layer will typically be madeusing a more heavily-doped semiconductor. If holes are the flowingcarrier in the active layer, then p-type doping of 1E16 cm-3, or 1E18cm-3, or even 1E20 cm-3, may typically be used. The thin (e.g. 2-20 nm)layer may be of an amorphous or polycrystalline material such as:PbSnTe; As2S3; As2Se3; SiO2; Si3N4; or SiOxNY.

In various embodiments, the active layer may be made by the followingprocesses: Synthesis: synthesizing colloidal quantum dots of generallythe same size, with typical size being in the range 1-10 nm. Oxygen andwater may be carefully excluded during the synthesis, typically throughthe use of a Schlenk line; or alternatively, one of oxygen and water maybe introduced at various stages of the synthesis in a controlledfashion. Nanoparticle washing: Optionally, using a nonsolvent (such asacetone, isopropanol, methanol) to cause the quantum dots toprecipitate; centrifuge including potentially at high rotational ratessuch as 10,000 or 13,000 rpm; redisperse in a new solvent (such aschloroform, toluene, hexanes, octane). Oxygen and water may be carefullyexcluded during the synthesis, typically through the use of a Schlenkline or a glovebox or other environmentally-controlled chamber; oralternatively, one of oxygen and water may be introduced at variousstages of the synthesis in a controlled fashion. Solution-phase ligandexchange: Optionally, using a nonsolvent (such as acetone, isopropanol,methanol) to cause the quantum dots to precipitate; redisperse in a newsolvent (such as acetonitrile, water, methanol, chloroform, toluene,hexanes, octane, butylamine, octylamine) that may incorporate at leastone species (e.g. ethanethiol, ethanedithiol, benzenethiol,benzenedithiol, hexanethiol, soluble salts such as those containingBismuth, Indium, Antimony, Sulfates such as Na2SO4); this new dispersionmay then be left for a brief period (e.g. 1-5 minutes) or a moreextended period (e.g. multiple days), typically either at roomtemperature or at elevated temperature (e.g. 60° C. or 80° C.), eitherin an inert environment (N2, Ar2) or an environment in which additionalreagents (O2, H2O, H2S, vapor-phase thiols) have been introduced; and,following this period, may optionally be precipitated and redispersed(including multiple times) as in (2) nano-particle washing. FilmCasting: A solution containing the colloidal quantum dots resulting from(1), or (1) followed by (2), or (1) followed by (3), or (1) followed by(2) followed by (3), may then be used to produce a thin solid film, ormultiple sequential layers of thin solid films. Methods includespin-casting, where a droplet of the solution is dispensed onto asubstrate or integrated circuit; optionally allowed to spread; and theninduced to spread and dry through the rotation of the substrate on whichit is placed, typically using a sequence of rotational acceleration,constant rotational velocity, and rotational deceleration, typicallyover minutes, and typically ranging from 500 to 10,000 rpm with 1000,3000, and 5000 rpm being typical values. Film Treatment: The resultantfilm (and/or each of the layers making up the multiple layers of thefinal multilayer film) may then be exposed to certain solutionenvironments and/or vapor-phase environments, in combination with (orpreceded by, or followed by, or both) elevation in temperature. Typicaltemperatures include room temperature, 60° C., 80° C., 100° C., 130° C.,150° C., 180° C., 200° C., 250° C., 300° C., 350° C., and 400° C.Typical times for various steps, both temperature steps and chemicaltreatment steps listed below, include 30 seconds, 1 minute, 3 minutes, 5minutes, 10 minutes, 30 minutes, 1 hour, 14 hours, and 3 days. Typicalsolution-phase treatments include: Immersing the substrate and film in asolution of anhydrous acetonitrile and anhydrous toluene or anhydrouschloroform containing 0.1%, 1%, 2%, 5%, 10%, 20%, or 30% by volume oneor more of the following chemicals: butylamine, ethanethiol,ethanedithiol, benzenethiol, benzenedithiol, hexanethiol, pyridine,hydrazine, Na2SO4, bismuth salts. Passing over the substrate and film,either while it is in a solution such as in (5)a. or not, a gas such asvapor-phase thiol, H2S, O2, H2O, or forming gas (H2:Ar or H2:N2 in aratio such as 3.5:97.5 or 5:95).

Methods of making contacts will now be discussed. The materials neededto form the conducting portion of the injecting and withdrawingcomponents may be formed using a variety of processes. In thefabrication of an integrated circuit that combines a CMOS siliconportion with the photoconductive overlayers described herein, thecontacts may be fabricated within a CMOS foundry (e.g. TSMC, SMIC, UMC)using preexisting, standard processes. The processes employed mayinclude evaporation sputtering, electroless deposition, orelectrodeposition. If a previous layer that provides the desired layoutfor the final contact is preexisting on the substrate, thenelectrodeposition or electroless deposition may be used to substantiallyreproduce this spatial pattern with additional layers deposited on top.

Methods of forming an optional top semiconducting or insulating layerwill now be discussed. The materials needed to form the semiconductingor insulating portion of the injecting and withdrawing components, whosepurpose is to enhance further the selectivity in favour of the flowingcarrier and against the trapped carrier, may be formed using a varietyof processes. In the fabrication of an integrated circuit that combinesa CMOS silicon portion with the photoconductive overlayers describedherein, the contacts may be fabricated within a CMOS foundry (e.g. TSMC,SMIC, UMC) using preexisting, standard processes. The processes employedmay include evaporation sputtering, electroless deposition, orelectrodeposition. If a previous layer that provides the desired layoutfor the contact is preexisting on the substrate, then electrodepositionor electroless deposition may be used to substantially reproduce thisspatial pattern with additional layers deposited on top.

Photoconductive photodetector pixels are sought that provide sensitivedetection of low levels of light include a pixel comprising: aninjecting contact; a withdrawing contact; and a photoconductive materialcomprising a colloidal quantum dot film that is in contact with each ofthe injecting contact and the withdrawing contact to form aphototransistor, wherein two types of carriers flow in thephotoconductive material comprising electron flow and hole flow, andwherein photoconductor material composition is designed to controllingflow of the two types of carriers and affect signal-to-noise ratios.

In an embodiment, dark current flows in response to electrons.

In an embodiment, light flow in response to excess holes is related to achange in conductivity of the photoconductive material

In an embodiment, a composition of a metal-semiconductor interfacebetween the contacts and the photoconductive material control which ifthe two types of carriers is a flowing carrier.

In an embodiment, a composition of the photoconductive material controlsa ratio of electron mobility to hole mobility.

In an embodiment, composition of the photoconductive material controlsequilibrium carrier density.

In an embodiment, composition of the photoconductive material determinescarrier lifetime, which improves lag.

Embodiments further include a colloidal quantum dot film photoconductivephotodetector pixel, comprising: a substrate layer; an active layercomprising photoconductive material, wherein the photoconductivematerial comprises two carrier types comprising a hole type carrier andan electron type carrier, wherein one of the types is a flowing carrierand the other type is a trapped carrier; and an injecting contactproximate the photoconductive material, wherein under biasingconditions, the injecting contact injects the flowing carrier into theactive layer with much greater relative efficiency than it withdraws thetrapped carrier from the active layer into the contact; a withdrawingcontact proximate the photoconductive material, wherein under biasingconditions, the withdrawing contact withdraws the flowing carrier fromthe active layer into the contact with much greater efficiency than itinjects the trapped carrier into the active layer; and one or moreoverlayers.

In an embodiment, the one or more overlayers is proximate thewithdrawing contact.

In an embodiment, the one or more overlayers is proximate the activelayer.

In an embodiment, the flowing carrier has a mobility of at least 1E-5cm2/Vs.

In an embodiment, the trapped carrier has a mobility that is at least10× less than that of the flowing carrier.

In an embodiment, the trapped carrier has a density of trap stateshaving lifetimes of between 1 microsecond to 1 second.

In an embodiment, the trapped carrier has a density of trap stateshaving densities ranging from 1E12 cm-3 to 1E22 cm-3.

In an embodiment, biasing conditions for the pixel include a bias on theinjecting contact, relative to the withdrawing contact, of a valueselected from a group comprising +0.1 V, +1 V, +1.8 V, and +2.8 V, whenthe flowing carriers are holes. The polarity is opposite if the flowingcarriers are electrons.

In an embodiment, biasing conditions for the pixel include a bias on theinjecting contact, relative to the withdrawing contact, of a valueselected from a group comprising −0.1 V, −1 V, −1.8 V, and −2.8 V, whenthe flowing carriers are electrons.

In an embodiment, the one or more overlayers comprise one or more of: apassivation layer; an encapsulation layer; transparent dielectrics;optical filters; other pixels comprising other active layers and othercontacts; and microlenses.

In an embodiment, the photoconductive material of the active layercomprises mutually-touching semiconductor nanoparticles comprisingnon-touching surfaces, and wherein the non-touching surfaces may becoated by one or more coatings selected from a group comprising: aninorganic material comprising an oxide or sulfate; and an organicmaterial comprising an organic ligand.

In an embodiment, the mutually-touching semiconductor nanoparticlescomprise a crystalline semiconductor selected from a group comprising:PbS, PbSe, PbTe; CdS, CdSe, CdTe; Si, Ge, C; In2Se3, In2S3, comprisingan alpha-phase or a beta-phase; InP; and Bi2S3.

In an embodiment, an inorganic material coating the non-touchingsurfaces of the nanoparticles comprises one or more materials selectedfrom a group comprising: PbSO4, PbO, PbSeO4, PbTeO4, and combinationsthereof; SiOxNy in various proportions; In2O3 in various proportions;sulfur, sulfates, and sulfoxides; carbon and carbonates such as PbCO3;and metals and semimetals comprising an excess of Pb, Cd, In.

In an embodiment, an organic material coating the non-touching surfacesof the nanoparticles comprises one or more materials selected from agroup comprising: Thiols comprising ethanethiol, ethanedithiol,benzenethiol, benzenedithiol; Amines comprising pyridine, butylamine,and octylamine; Hydrazine; and Carboxylates comprising oleic acid.

In an embodiment, a dimension of the active layer perpendicular to adirection of incident of light comprises between 100 nm and 3000 nm, andwherein a thickness of the active layer is chosen such that wavelengthsof light of interest are substantially absorbed.

In an embodiment, the injecting contact and the withdrawing contact aremade of the same material.

In an embodiment, the injecting contact and the withdrawing contact aremade of different materials.

In an embodiment, at least one of the injecting contact and thewithdrawing contact comprise a conductive material that comprises one ormore materials selected from a group comprising: a metal; adegenerately-doped semiconductor; and a combination of a metal and adegenerately-doped semiconductor.

In an embodiment, the flowing carrier comprises holes, and wherein theinjecting contact comprises one or more materials selected from a groupcomprising: Au, Pt, Pd, Cu, Ni, NiS, TiN, TaN, p-type polysilicon, andp-type amorphous silicon.

In an embodiment, the flowing carrier comprises electrons, and whereinthe injecting contact comprises one or more materials selected from agroup comprising: Al, Ag, In, Mg, Ca, Li, Cu, Ni, NiS, TiN, TaN, n-typepolysilicon, and n-type amorphous silicon.

In an embodiment, at least one of the contacts comprises: a first layercomprising one or more materials selected from a group comprising: ametal; a degenerately-doped semiconductor; and a combination of a metaland a degenerately-doped semiconductor; and a second layer comprisingone or more materials selected from a group comprising: a semiconductor;and a material having a bandgap.

In an embodiment, the second layer comprises mutually-touchingsemiconductor nanoparticles, and wherein p-type doping is used whenholes are the flowing carrier in the active layer.

In an embodiment, the second layer has a thickness of approximately 5 nmto 50 nm.

In an embodiment, the second layer has p-type doping of a concentrationselected from a group comprising: 1E16 cm-3; 1E18 cm-3; and 1E20 cm-3.

In an embodiment, the second comprises one or more of an amorphousmaterial and a polycrystalline material selected from a groupcomprising: PbSnTe; As2S3; As2Se3; SiO2; Si3N4; and SiOxNY.

Embodiments further include a method of making a photoconductivephotodetector that achieves sensitive detection of low levels of light,the method comprising: forming an active photoconductive layercomprising synthesizing colloidal quantum dot having a size in a rangeof 1 nm to 10 nm; producing at least one thin solid film from a solutioncontaining the colloidal quantum dots; treating the at least one thinsolid film, comprising, exposure to at least one of solution-phaseenvironments and vapor-phase environments; and elevation in temperature.

An embodiment further comprises forming contacts, including forming aconductive layer of the contacts by one or more processes selected froma group comprising evaporation sputtering, electroless deposition, andelectrodeposition.

An embodiment further comprises forming a semiconducting layer of thecontacts by one or more processes selected from a group comprisingevaporation sputtering, electroless deposition, and electrodeposition.

An embodiment further comprises: nonparticle washing using a nonsolventto cause the quantum dots to precipitate; centrifuging the quantum dots,comprising centrifuging at a high rotational rate; and redispersing thequantum dots in a new solvent.

In an embodiment, the high rotational comprises rates in a range of10,000 rpm to 13,000 rpm.

An embodiment further comprises a solution-phase ligand exchangecomprising: using a nonsolvent to cause the quantum dots to precipitate;redispersing the quantum dots in a new solvent that incorporates atleast one species; and leaving the new dispersion for a period.

In an embodiment, the period comprises a brief period of 1 minute to 5minutes, and a more extended period of multiple days, and wherein thenew dispersion is left at a temperature comprising room temperature andelevated temperature comprising 60° C. and 80° C.

An embodiment further comprises: leaving the new dispersion in anenvironment comprising an inert environment, and an environment in whichadditional reagents have been introduced; and precipitating andredispersing the colloidal quantum dots.

In an embodiment, producing at least one thin solid film furthercomprises one or methods chosen from a group comprising spin-casting,wherein, a droplet of the solution is dispensed onto surface comprisingone of a substrate and an integrated circuit; and the droplet is inducedto spread and dry through the rotation of the surface.

In an embodiment, rotation of the surface comprises a sequence ofrotational acceleration, constant rotational velocity, and rotationaldeceleration over minutes, wherein rotation rates range from 500 rpm to10,000 rpm.

In an embodiment, elevation in temperature in treating the at least onethin solid film comprises one or more temperatures selected form a groupcomprising room temperature, 60° C., 80° C., 100° C., 130° C., 150° C.,180° C., 200° C., 250° C., 300° C., 350° C., and 400° C.

In an embodiment, elevation in temperature is for a period selected froma group comprising 30 seconds, 1 minute, 3 minutes, 5 minutes, 10minutes, 30 minutes, 1 hour, 14 hours, and 3 days.

In an embodiment, exposure to solution-phase environments comprisesimmersing in a solution of anhydrous acetonitrile and one of anhydroustoluene and anhydrous chloroform containing 0.1%, 1%, 2%, 5%, 10%, 20%,or 30% by volume one or more of chemicals selected from a groupcomprising butylamine, ethanethiol, ethanedithiol, benzenethiol,benzenedithiol, hexanethiol, pyridine, hydrazine, Na2SO4, and bismuthsalts.

In an embodiment, exposure to vapor-phase environments comprises passingover the thin solid film a gas comprising one or more of as vapor-phasethiol, H2S, O2, H2O, and forming gas, including H2:Ar or H2:N2 in aratio comprising 3.5:97.5 or 5:95.

In an embodiment, the exposure to vapor-phase environments occurs whilethe thin film immersed in a solution of anhydrous acetonitrile and oneof anhydrous toluene and anhydrous chloroform containing 0.1%, 1%, 2%,5%, 10%, 20%, or 30% by volume one or more of chemicals selected from agroup comprising butylamine, ethanethiol, ethanedithiol, benzenethiol,benzenedithiol, hexanethiol, pyridine, hydrazine, Na2SO4, and bismuthsalts.

Photodetectors compatible with video frame rates, and possessingphotoconductive gain, are now discussed. Embodiments described hereininclude a photoconductive photodetector in which substantially a singlechemical species has associated with it a substantially single energydepth and thus, at a given temperature, a substantially single trapstate lifetime, and thus a substantially single temporal componentassociated with the rise and fall of photocurrent during incidentoptical transients. Embodiments include photoconductive photodetectorswhere the single chemical species is PbSO3 (lead sulfite); the singleenergy depth is approximately 0.1 eV; at room temperature thesubstantially single trap state lifetime is ˜30 milliseconds; thesubstantially single temporal component associated with the rise andfall of photocurrent is ˜30 milliseconds. In embodiments the followingare not substantially included into the photoconductive medium: leadsulfate PbSO4, having depth 0.3 eV or greater, and having transientcomponent of order seconds; lead carboxylate, having depth 0.2 eV orgreater, and having transient component of order half a second or more.

Note also that other chemical species may be present if they do not haveassociated with them trap states. For example PbS may be used as thebasis for the photoconductive semiconductor medium; and organic ligandssuch as ethanethiol, ethanedithiol, butanethiol, butanedithiol,hexanethiol, hexanedithiol, dodecanethiol, and dodecanedithiol, andtheir complexes with Pb, may all be included.

FIGS. 41-51 illustrate embodiments that include controlling temporalresponse of photoconductive photodetectors via selective introduction ofsurface trap states.

Photoconductive photodetectors have recently been shown to exhibit highgains (>1000) and outstanding sensitivities (D*>10¹³ Jones). Oneostensible disadvantage to exploiting photoconductive gain is that thetemporal response is limited by the release of carriers from trapstates. Embodiments include introduction of specific chemical species oncolloidal quantum dot surfaces that introduce only a single, desiredtrap state having a predetermined lifetime. Embodiments include devicesthat exhibit an attractive photoconductive gain (>10) combined with aresponse tie (˜25 milliseconds) useful in imaging. Methods of achievingthis include providing for a substantially single surface species—leadsulfite—while eliminating the presence of lead sulfate and leadcarboxylate. Embodiments thus include photodetectors that preserve theoutstanding sensitivity of these devices, achieving a specificdetectivity of 10¹² Jones in the visible, while generating a temporalresponse suited to imaging applications.

Temporal response is important in photodetection. If the response of aphotodetector to an optical transient exceeds the frame period, thenlag, or ghosting, will be perceptible in the image. Conventional imagingapplications typically require frame rates in the range of 10, 15, 30,or 60 frames per second. Temporal responses having time constants in therange of tens of milliseconds are thus required.

There exists a high degree of interest in novel materials, and novelprocessing methods, for the realization of innovative imaging systems.Solution-processed optoelectronic materials offer large area at lowcost⁴; the benefits of physical flexibility; the 100% fill factorassociated with a top-surface photodetector technology⁵; and thecapacity to sense wavelengths, such as those in the short-wavelengthIR⁶, not accessible to conventional electronic materials such assilicon.

Certain embodiments of colloidal quantum dot photodetectors haveexhibited either superb sensitivities (D*>1E13 Jones) but slow response(hundreds of millisecond transients); or rapid response (MHz and abovebut low sensitivity (D*<10¹⁰ Jones)⁸.

Embodiments now described include careful control over materialscomposition that results in engineering of the temporal response ofphotoconductive photodetectors to achieve outstanding sensitivity andacceptable temporal response simultaneously.

Photoconductive gain is given by τ_(c)/τ_(t), where τ_(t) is the timefor the flowing carrier to transit the extent of the device, and τ_(c)is the carrier lifetime. From a sensitivity point of view alone, thisargues for longer trap state lifetimes. However, the transient responseis directly determined by the carrier lifetime. The challenge ofpractical photoconductive photodetector design is thus to establish asuitable balance between gain and transient response; and to controlmaterial composition with care to implement the resultant design.

Energy levels associated with trap states in PbS colloidal quantum dotphotodetectors having gains of order hundred A/W have been investigated.In cases, three sensitizing centers the energy levels of which residedapproximately 0.1, 0.2 and 0.34 eV from the conduction band, resulted incarrier lifetimes of ˜60 ms, 300 ms and 2000 ms (FIG. 41). Though theshortest lifetime of 30 ms is suited for many imaging applications, thelonger ones, which dominate at lower optical intensities in view oftheir lower energies, introduce unacceptable lag.

In embodiments, photoconductive devices were fabricated by spincoatingas-synthesized nanocrystals, the first excitonic peak of which was at790 nm, capped with oleic acid on pre-patterned interdigitated goldelectrodes. The thickness of the devices reported herein was keptconstant around 250 nm. The active area of the device is determined bythe 5 μm separation of the electrodes and multiplied by their 3 mmlength. For illumination a red LED was used at 642 nm with opticalintensity of 3.1 μW/cm² unless otherwise stated. The bias applied to thedevices studied herein was 10 V, corresponding to an electric field of 2V/μm. Photoconductive measurements were performed with devices loaded ina cryostat under vacuum conditions so that oxygen and moisturechem-absorption effects are eliminated.

XPS analysis of butylamine (BA) treated nanocrystals revealed theexistence of lead sulfate (PbSO₄), lead sulfite (PbSO₃), and leadcarboxylate attributable to oleic acid ligands attached to thenanoparticles' surfaces. XPS analysis of the S2p signal yields a peak at165.5 eV attributable to PbSO₃ and a peak 167.8 eV resulting from PbSO₄(FIG. 42 b) whereas Pb4f signal analysis revealed oxidized statesattributable to PbSO₄ and PbSO₃ at 138.5 eV and a highly oxidized stateof Pb found at 139.1 eV attributable to Pb-carboxylate (FIG. 42 a). Toverify this last finding, we carried out XPS on Pb-oleate (the same usedfor PbS nanocrystal synthesis), revealing a single peak of Pb at 139.1eV (see supplementary material for detailed analysis of XPS results).

Lead carboxylate peak (attributable to the oleic acid—Pb bond) was thencorrelated with a corresponding sensitizing trap state having a specifictemporal response. We treated nanocrystal films with a 30% by volumesolution of formic acid in acetonitrile to exchange the long oleic acidligand with a shorter one. In so doing we reduced internanoparticlespacing while preserving the carboxylate moiety bound to Pb atoms on thenanocrystal surface. In this way, we transformed insulating devices intophotoconductive detectors. Temporal measurements of photocurrentresponse revealed a main time constant of ˜400 ms (FIG. 41) and also afaster component with time constant ˜33 ms. XPS revealed an oxidizedcomponent to the Pb4f signal at 139.1 eV characteristic of thePb-carboxylate group, as illustrated in FIG. 42 a as well as a signal at138.5 eV arising from the existence of PbSO₃ as verified by the S2psignal (FIG. 42 b). This evidence suggests that either Pb-carboxylate orPbSO₃ serves as a sensitizing species having an (undesirably long-lived)˜420 ms time constant.

Complete removal of the oleate ligands is therefore required in order toassign the 400 ms time constant to a specific oxide species. We sought aligand, short enough to promote transport, and lacking carboxylatefunctionality. To make the replacement of the carboxylate-terminatedligand thermodynamically favourable, we posited that we would require anendgroup that would bind to the Pb more strongly than Pb-carboxylate. Weselected ethanethiol for its short length and thiol moiety expected tobind strongly with Pb. We treated the devices by dipping in 40% byvolume ethanethiol in acetonitrile for approximately 5 minutes. Weremoved the device from solution, rinsed with acetonitrile, and dried.

From the absence of Pb4f peak at around 139.1 eV (FIG. 42 a) we concludethat oleate ligands were indeed entirely removed from the nanocrystalsurface. Thiol treatment also removed polysulfites and lead sulfate fromthe nanocrystal surface leaving PbSO₃ as the sole oxidized species (FIG.42 b). Transient photocurrent measurements showed that ET treatednanocrystal films exhibited a single transient component having a ˜27 mstime constant at room temperature (FIG. 41).

We found that PbS nanocrystal films having lead sulfate (PbSO₄), leadsulfite (PbSO₃), and lead carboxylate manifested photocurrent decayshaving time constants ˜2 s, 300 ms and ˜60 ms. PbS nanocrystalspossessing lead carboxylate and PbSO₃ exhibited a photocurrent decaywith time constants ˜420 ms and ˜33 ms. Thiol treated nanocrystals onwhich only lead sulfite was present exhibited a single photocurrentrelaxation time constant of ˜27 ms. We confirmed the association betweenthe sulfate and the long two-second time constant ageing a thiol-treateddevice in ambient for several hours. We found that a slow componentemerged having the several-second time constant, and found using XPSthat significant growth of lead sulfate had taken place (seesupplementary material).

We sought to investigate in greater detail the energy level associatedwith the desired 25 millisecond trap state. FIG. 43 a shows thephotocurrent as a function of temperature. At low temperatures, wherethe sensitizing centers are not thermally quenched, and therefore thedevices are fully sensitized, responsivity increases with temperaturefollowing the mobility thermal activation of 0.14 eV similarly reportedfor such materials. At elevated temperatures, photocurrent quenchingtakes place as a result of thermal deactivation of the sensitizingcenter. The slope of the quenching rate with temperature (inset of FIG.43 a) yields an activation energy 0.16 eV from the conduction band. Thisagrees well with previous reports of the shallowest center in butylaminetreated PbS nanocrystal photodetectors. We ascertained the sameactivation energy using an independent method, investigating thedependence of the photocurrent transient on temperature¹². Using thismethod we ascertained the sensitizing center's energy to be 0.12 eVbelow the conduction band, in reasonable agreement with the responsivityquenching results (FIG. 43 b).

Results of full characterization of the thiol-treated device are nowdiscussed, focusing on its applicability to imaging applicationsrequiring the combination of sensitivity and acceptable temporalresponse. The spectral responsivity is reported in FIG. 43 a.Responsivity was measured at intensity levels of ˜300 nW/cm² using a 642nm LED. The device was biased to 10 V. We measured the noise current inthe device¹⁵ and plot in FIG. 43 a the detectivity, D*. Sensitivity isretained without compromise: D* greater than 10¹² Jones is obtainedacross the visible spectrum. FIG. 43 b also illustrates the deviceresponsivity and detectivity as function of modulation frequency. Theabsence of long lived trap states is evident from the flat response ofresponsivity at frequencies below 5 Hz where the sensitizing centersassociated with the ˜400 ms and ˜2 s time constants would determine theresponsivity roll-off.

Embodiments described herein thus provide fine-tuning of deviceperformance at the macroscopic level via careful manipulation of theexistent material species on the nanocrystal surface. We showed that wecan transform a very slow photoconductive photodetector withphotocurrent decay taking place within several seconds to a fasterphotoconductor with photocurrent time constant in the order of 25 ms. Weachieved this without sacrificing in photoconductive gain by furtherreducing the internanoparticle spacing. This work demonstrates also thatthorough investigation and control of the nanocrystal surface materialsenables tailoring of the optoelectronic properties that could findapplications in progressing not only photoconductivity as illustratedherein but also optical emission or photovoltaics.

FIGS. 44 a and 44 b show spectral responsivity an detectivity of devicesas labeled in the figure.

FIG. 45 is a summary of correlation between oxide species andphotocurrent time as labeled in the figure.

FIGS. 46 a and 46 b show XPS analysis of variously treated PbSnanocrystal films as labeled in the figure.

FIG. 47 is a diagram illustrating observed performance of a Pb-oleateembodiment as labeled in the figure.

FIGS. 48 a and 48 b illustrate observed performance of Butylaminetreated nanocrystals as labeled in the figure.

FIGS. 49 a and 49 b illustrate observed performance of Formic Acidtreated nanocrystals as labeled in the figure.

FIGS. 50 a and 50 b illustrate observed performance of Ethanethioltreated nanocrystals as labeled in the figure.

FIG. 51 is a diagram illustrating observed performance of Ethanethioltreated nanocrystals aged in ambient as labeled in the figure.

Alternative embodiments and methods of making high-performancesolution-processed photodetectors for imaging applications are nowdiscussed. Photoconductive photodetectors provide tremendoussensitivities to low light—D* (normalized detectivity) greater than 1E12Jones have been shown—however they come at the expense of dark current.

Photodiodes, in contrast, can be operated unbiased, and thus can haveessentially zero dark currents. Embodiments include a photodiode-basedphotodetector having high external quantum efficiency; low dark current(<0.1 nA/cm2); 3 dB bandwidth>1 kHz (already well-suited to imaging)

Embodiments include a device consisting of a stack of (a) Adeep-work-function electrical contact; (b) A colloidal quantum dotsolid; (c) A shallow-work-function electrical contact At least one ofthe two contacts is substantially transparent. Embodiments include thepreceding devices where (a) Consists of Au, Pt, Pd, Ni, Cu, or Au-rich,Pt-rich, Pd-rich ITO, or deep-work-function ITO; where (b) Consists ofcolloidal quantum dots such as PbS, CdS, In2S3, In2Se3, Bi2S3, Bi2Se3,CuInGaSe; organic ligands such as oleic acid (or other carboxylicacids), benzenethiol (or other thiols), or butylamine (or other amines);bidentate organic ligands such as butanedithiol, benzenedithiol,ethanedithiol, hexanedithiol; oxides, sulfates, and hydroxides of thespecies making up the colloidal quantum dot; (c) Consists of Al, Mg, Ca,or deep-work-function ITO. Embodiments include devices wherein thecolloidal quantum dot solid is substantially fully depleted. Embodimentsinclude devices wherein the colloidal quantum dot solid contains aregion that is substantially fully depleted; and also a region that issubstantially quasi-neutral. Embodiments include devices where theexternal quantum efficiency is greater than 40%, or 60%, or 80%, or 90%;where the dark current density is approximately 0.1 nA/cm2, or 0.01nA/cm2, or 1 pA/cm2, or 0.1 pA/cm2; where, following the turn-off ofincident illumination, the device returns to its dark current valuewithin 10 milliseconds, or 1 millisecond, or 0.1 milliseconds, or 10microseconds, or 1 microsecond, or less; where, following the turn-on ofincident illumination, the device rises to its steady-statelight-current value within 10 milliseconds, or 1 millisecond, or 0.1milliseconds, or 10 microseconds, or 1 microsecond, or less.

Embodiments include solution-processed photodiode photodetector witha >60 kHz bandwidth, D*>1e12 cm.√{square root over (Hz)}.W⁻¹, and darkcurrent density of 0.1 nA.cm⁻². This represents a >3300 fold improvementin response speed and >11 order-of-magnitude reduction in dark currentdensity over the most sensitive solution-processed photodetectors, and a100,000 fold improvement in sensitivity over the fastestspectrally-tunable solution-processed photodetectors. This performancewas achieved through optimization of the inherently fast photodiodedetector architecture for increased sensitivity. Device operation isexamined in detail and explained in terms of photogenerated carriertransport.

Solution-processed semiconductors have demonstrated great potential forfabrication of highly-sensitive photoconductive photodetectors operatingin both the visible and the infrared. However, these devices can oftenrespond slowly to changes in illumination. Solution-processedphotodetectors based on a photodiode architecture offer broad-bandwidthand highly-uniform frequency response, but are limited by lowsensitivity.

FIG. 52 shows the bandwidth and sensitivity of examples of the fastestand most-sensitive solution-processed photodetectors reported to date.

The use of colloidal quantum dots (CQD) offer benefits over organicsolution processed semiconductors: spectral functionality spanning boththe visible and infrared, and direct control over absorption onsetthrough the quantum size effect. Operation at IR wavelengths allowsdetection of light transmitted through atmospheric, biological, andmaterials absorption windows, dramatically increasing the range ofpotential applications of a photodetector. As the absorption onset of asemiconductor is moved toward longer wavelengths, the rate of thermalnoise generation increases, limiting the sensitivity of a photodetector.By tuning the absorption onset to include only the wavelengths ofinterest, thermal noise at longer wavelengths is rejected.

Additional benefits realized with the photodiode architecture includezero or low voltage operation, very low power dissipation, and ahighly-linear signal response to changes in illumination intensity andmodulation frequency. Low dark current allows CQD photodiodes to be useddirectly in place of crystalline detectors, as dark-current andphotocurrent densities are very similar. In contrast, previouslydemonstrated photoconductive detectors have very large dark andphotocurrent densities, requiring the development of new signalprocessing circuitry capable of extracting high quality signals from thelarge currents.

Solution-processable semiconductors offer low-cost, large-area, flexiblestructures, and compatibility with a wide range of substrates, enablingdirect integration into emerging technologies such as integrated organiccircuits, micro-fluidics, and integrated optical circuitry, as well ascommercial microelectronics. Solution-processed semiconductors havedemonstrated great potential for fabrication of highly-sensitivephotodetectors operating in both the visible and the IR. However, thesephotoconductive devices respond very slowly to changes in illumination.In contrast, solution-processed photodetectors based on a photodiodearchitecture offer broad-bandwidth and highly-uniform frequencyresponse, but are limited by low sensitivity.

The structural compatibility of solution-processed semiconductors withsubstrates ranging from flexible plastics to metals, glasses and othersemiconductors arises from the absence of the crystal lattice matchingrequirements inherent in crystalline semiconductors. Solution-processedsemiconductors include organic materials such as polymers andsmall-molecules, and organic-inorganic hybrids such as colloidal quantumdots.

The sensitivity of a detector describes its ability to resolve very lowintensity optical signals. This limit is characterized by the noiseequivalent power (NEP=i_(n)/R_(i)), in units of Watts, and isproportional to the total internal noise current (i_(n)) in the devicedivided by its responsivity (R_(i))—the electrical current response tooptical excitation. NEP represents the amount illumination required togenerate a signal equal to the internal noise of the detector. Thesensitivity of detectors is commonly reported as a normalizeddetectivity (D*=√{square root over (AΔf)}/NEP), in units of cm.√{squareroot over (Hz)}.W⁻¹ (Jones), to allow direct comparison of detectorswith different active areas (A) and noise bandwidths (Δf).

The bandwidth of a photodetector is typically characterized by its 3 dBfrequency (F_(3dB))—the illumination modulation frequency where theresponse of the detector is reduced to 50% of its maximum value. While abandwidth of ˜20 Hz is sufficient for the lowest bandwidth photodetectorapplications (i.e. video imaging arrays), it remains too slow for themajority of photodetector applications. Additionally, the non-uniformityof the frequency response of these slow photodetectors distortsbroad-bandwidth signals during detection^(6,7), limiting applicationsrequiring quantitative signal analysis. The only report of a fast CQDdetector (F_(3dB)˜50,000 Hz) demonstrated a sensitivity of approximately1e7 cm.√{square root over (Hz)}.W⁻¹—five orders of magnitude lower thancrystalline semiconductor photodetectors.

One disadvantage of certain existing sensitive CQD photodetectors ishigh dark current densities (>10 mA.cm⁻²). Combined with high operatingbiases (up to 100 V), photoconductive CQD detectors consume largeamounts of power and require the development of specialized signalprocessing circuitry capable of extracting high-quality signals from thelarge currents. This may be a limiting factor in common photodetectorapplication such active matrix imaging arrays, where complexity of thecircuitry allocated to individual pixels is limited by the pixel area.In contrast, solution-processed photodiode detectors have significantlylower dark current densities (1 to 20 nA.cm⁻²) and operating voltages (0to 6 V), allowing integration with existing signal processing circuitry.

The absorption onset of CQDs is limited only by the bulk bandgap oftheir constituent semiconductor material, and can be tuned through acontinuous range of wavelengths through the quantum size effect. CQDabsorption onsets have been demonstrated at wavelengths up to 2000 nmfor PbS CQDs¹¹, and or 3000 nm for HgCdTe CQDs. In contrast, theabsorption onset of organic semiconductors is fixed by theircomposition, and has so far been limited to wavelengths <1000 nm.Operation at IR wavelengths allows detection of light transmittedthrough atmospheric, biological, and other materials absorption windows,dramatically increasing the range of potential applications in remotesensing, imaging, metrology, and communications. The ability to limitspectral sensitivity is also important. As the absorption onset of asemiconductor is moved toward longer wavelengths (typically by reducingthe energy bandgap), internal thermally generated noise in theincreases, limiting the sensitivity of the photodetector. CQDs offerabsorption over a wide range of wavelengths while maintaining precisecontrol of absorption onset and long-wavelength thermal noise rejection,making them a compelling material for the fabrication of semiconductorphoton detectors.

The photodetector presented in this report operates as a photodiode,unlike many previous CQD photodetectors, which operate asphotoconductors. The CQD photodiode is composed of a thin film of PbScolloidal quantum dots sandwiched between planar ITO and Al electrodes,as shown in the inset of FIG. 53 (a). Light incident through the glasssubstrate and transparent ITO contact generates electrons and holes inCQD film which are collected at the Al and ITO contacts, respectively.The energy band diagram in FIG. 55 shows the Schottky barrier formed atthe Al/PbS CQD interface, and the built-in potential derived from thedifference in work function between the CQDs and the metal contact.Charge transfer between the semiconductor and the metal results in theformation of a wide depletion region (DR) in the CQD film, while theremaining volume of CQD film is a quasi-neutral region (QNR) of p-typesemiconductor with no net charge or electric field. The large potentialbarrier in the valence band limits majority carrier (hole) injectionfrom the Al contact, resulting in highly rectifying dark I-Vcharacteristics. The built-in potential is the distinguishing featurebetween photodiode and photoconductive detectors, and provides efficientphotocarrier collection at zero or low-bias operation, with minimal darkcurrent.

We synthesized PbS CQDs with a diameter of ˜6 nm, effectively increasingthe energy bandgap of PbS from 0.42 eV to 0.86 eV through sizequantization¹⁰. This effective bandgap corresponds to a ground-stateexcitonic absorption feature at 1450 nm and can be seen in the CQD filmabsorption spectra of FIG. 53 (a). As synthesized, the CQDs were cappedwith 2.5 nm long oleate ligands, which provided colloidal stability andpassivated the nanocrystal surfaces. To reduce inter-particle spacing infilms and improve carrier transport, the original ligands were partiallyexchanged in favor of shorter primary butylamine ligands using asolution phase ligand exchange⁶. CQD films (˜350 nm thick) weredeposited from solution by spin-casting. Following film deposition, asecond, solid state ligand exchange was performed by immersing the filmsin a solution of benzene dithiol (BDT) in acetonitrile. This exchangeeliminates excess butylamine in the CQD film, which was observed to bechemically reactive with the Al contact. Following BDT treatment, Alcontacts were deposited by thermal evaporation and the complete devicewas exposed to an air atmosphere.

BDT treatment increased photodiode lifetime from approximately 4 hoursto over 2 months and dramatically reduced short-circuit dark currentdensities from ˜100 nA.cm⁻² to 0.1 nA nA.cm⁻². The noise associated withthese dark currents previously limited the detectivity of the CQDphotodiodes to ˜1e0 cm.√{square root over (Hz)}.W⁻¹. The BTD treatmentalso affected the Al/PbS CQD Schottky barrier, initially resulting in asubstantial decrease in diode I-V characteristics. It was hypothesizedthat BDT chemically reduced the PbS CQDs, suppressing the p-typesemiconductor characteristics derived from the oxidation of PbS¹⁹, andconsequently reduced the built-in potential of the Schottky barrier.Photodiodes subsequently exposed to an air atmosphere for several hourswere found to maintain the highly reduced short-circuit dark current,while regaining diode I-V characteristics observed prior to BDTtreatment. This observation suggested that re-oxidation of the PbS CQDsmay occur following BDT treatment.

The external quantum efficiency (EQE) and normalized zero-bias shuntresistance (RoA) describe the fundamental components of photodiodeperformance—photogenerated carrier collection efficiency and internalnoise. (In the absence of illumination or applied bias, noise inphotodiodes originates entirely from thermal noise, and can becalculated, i_(n)=√{square root over (4 k_(b) T/R_(o))}, based on theeffective shunt resistance of the photodiode at zero bias (R_(o)),Boltzman's constant (k_(b)), and the temperature (T)). Starting with aCQD synthesis known to produce high RoA and EQE in untreatedphotodiodes, CQD batch preparation, BDT treatment time, andpost-treatment air annealing time were controlled to optimize deviceperformance.

EQE was observed to increase steadily with air anneal time after BDTtreatment in all CQD batches, as shown in FIG. 54. Further improvementsin EQE were achieved using accelerated annealing in high-humidityconditions (started at 16 hours in Batch 1 and 44 hours in Batch 2),yielding ˜15% EQE at the first excitonic absorption feature. To producea highly sensitive photodiode, RoA must also be as large as possible.Untreated CQDs produced Schottky barriers with RoA˜1e5 Ω.cm².Immediately after BDT treatment, RoA decreased by approximately 2 ordersof magnitude, as shown in FIG. 54. While air annealing improved EQE inall CQD batches, only batches with a recent (<7 days) ligand exchangedemonstrated restoration of RoA with air annealing (Batch 1 in FIG. 54).

The effect of BDT treatment time was also examined. Increasing BDTtreatment time continuously improved RoA, but EQE was optimized for 60minute BDT treatments, as shown in FIG. 54. Further exposure to BDTresulted in a reduction of steady-state EQE. Analysis of the transientphotocurrent of devices with 120 minute BDT treatments showed a rapiddecay of the initial photocurrent, consistent with carrierrecombination. This phenomenon was not observed in devices with shorterBDT treatment times.

We characterized the dark current, photocurrent response, and darkcurrent noise of the optimized CQD photodiodes using illumination ofvarying wavelength, intensity, and modulation frequency, and over arange of operating temperatures.

FIG. 53 (a) shows external quantum efficiency (at 295 K) and normalizeddetectivity (at 250 K) as a function of wavelength. An EQE of 17% isachieved at 1450 nm and reaches a maximum of 52% at 580 nm.Photoresponse is measurable to 1800 nm, limited by the CQD absorptiononset defined by quantum-size effect. D* is >1e12 Jones at 1450 nm fortemperatures below 255K and >1e12 Jones at 1120 nm for temperaturesbelow 280K. The shape of the EQE spectrum follows the net absorptionspectrum of the CQD film (see FIGS. 57-66, for example). The peak in theabsorption and EQE at 1450 nm corresponds to the first CQD excitonicabsorption feature while peaks in the absorption and EQE at shorterwavelengths are the result of Fabry-Perot interference effects in thethin CQD film. The absorption coefficient at 1550 nm is 1.05e4 cm⁻¹, ascalculated from the net CQD film absorption and film thickness. FIG. 53(b) shows photocurrent density as function of irradiance. The responseis linear within 6% over 4 decades of irradiance—an improvement overphotoconductive CQD detectors where photoresponse depends on trap stateoccupancy and thus, illumination intensity.

FIG. 53 (c) shows normalized photocurrent as a function of illuminationmodulation frequency. The 3 dB frequency is 10.7 kHz at zero bias and1.95 μW.cm⁻². The response is nearly flat up to the appearance of a poleat 1 kHz. A second pole appears at 50 kHz. These poles correspond to thetime required to reach the steady state in the QNR and the transit timeof the DR, ˜500 μs and ˜10 μs, respectively, as shown in FIGS. 56 (a)and (b). FIGS. 53 (d) and (e) show an exponential dependence of the 3 dBfrequency on irradiance and a sublinear dependence of the 3 dB frequencyon reverse bias. The maximum observed 3 dB frequency was 61.2 kHz at−1.0 V bias and 17.9 μW.cm⁻² illumination.

The transient response to stepwise changes in illumination is used toelucidate the physics underlying the operation of the photodiode. FIG.56 (a) shows the photocurrent response to a 500 μs square illuminationpulse at photodiode biases of 0.0, −0.5, and −1.0V. At each bias, thetransient response is composed of two distinct components—an initial,fast, linearly increasing component; and a slower, exponentiallyincreasing component. The rise and fall characteristics of thephotocurrent are symmetric.

A model may be derived for the photocurrent response based on classicalcarrier transport. The fast photocurrent component is attributed tocarriers generated in the depletion region (DR) (G_(DR) in FIG. 57) andquickly swept out by a drift current proportional to the built-inelectric field (E). The total rise time of this component is equal tothe DR transit time t_(tr)=w_(DR)/(μ_(h)E), where μ_(b) is the holemobility. The slower component is attributed to electrons generated inthe quasi-neutral region (QNR) (G_(QNR) in FIG. 55) which must diffuseto the DR. The rise time of this component is the time required forgeneration, diffusion, and recombination processes in the QNR to reach asteady state, and is dependent on the width of the quasi-neutral region(w_(QNR)) and inversely dependent on the electron diffusion coefficient(D_(e)). A numerical model may be constructed to test the capacity ofclassical transport and the semiconductor continuity equations todescribe the photoresponse of the CQD photodiode (see 68-76, forexample). Using measured values for all physical parameters in thecontinuity equations, solutions for the electron and hole densities as afunction of time and position were found, and used to calculate theelectron diffusion and hole drift currents. As shown in FIG. 56 (a),with increasing reverse bias, both the measured and simulated responsesshow an increase in the magnitude of the fast photocurrent component anda decrease in the time required for the slow current component currentto reach steady state. The magnitude of the fast component increaseswith reverse bias—a result of the increasing width of the depletionregion (w_(DR)) with reverse bias, (see FIGS. 57-66, for example) and aconcatenate increase in the number of photocarriers generated in the DR.An increase in w_(DR) result in decrease of w_(QNR) and a reduction inthe time required to reach steady state in the QNR. Both measured andsimulated photocurrent show increasing response speed in the slowcurrent component—a trend consistent with the observations of increasing3 dB frequency with increasing reverse bias, as shown in the secondinset of FIG. 53 (b).

FIG. 56 (b) shows a detailed view of the fast and slow photocurrentresponse to the onset of irradiances of 17.9, 107 and 492 μW.cm⁻². Thecurrent response is normalized to allow comparison of the transientresponse at each irradiance. Both measured and simulated results show anincrease in the response speed of the slow current component withincreasing irradiance, while the fast current component remainsessentially unchanged. Decreasing carrier lifetime with increasingirradiance, (see FIGS. 57-66, for example) reduces the time required forthe QNR to reach steady state, thus increasing the response rate of thediffusive current component. This trend is consistent with theobservations of increasing 3 dB frequency with increasing illumination,as shown in the first inset of FIG. 53 (b).

Means of realizing the aforementioned CQD photodetectors are nowdiscussed. PbS CQDs with an excitonic peak ˜1500 nm were prepared byinjection of 2.0 mmol bis(trimethylsilylsulphide) into a reaction flaskcontaining 4.0 mmol lead oxide (0.9 g), 9.5 mmol oleic acid (2.67 g) and18.8 mmol octadecene (4.73 g) at 120 C. After the injection, thereaction was quenched by moving the flask to an ice-water bath. Thesynthesis was carried out under inert conditions using a Schlenk line.The final PbS oleate-capped CQDs were isolated from any remainingstarting materials and side products by precipitating with acetone andre-dissolving in toluene, repeated 2×. Solution-phase ligand exchangerequired precipitating the CQDs with MeOH and redissolving in toluene 2×before a final precipitation with MeOH and res-dissolving in primarybutylamine. The mixture was left for 3 days at room temperature, thenprecipitated with isopropanol and redispersed in octane. All processingwas carried out in a glove box with an N2 atmosphere. Films (350nm-thick) were formed by spin-coating CQDs suspended in octane ontocommercial glass substrates coated with conductive indium-tin oxide(ITO). After film deposition, the CQDs were treated in a 5 mg/mlsolution of benzene dithiol (BDT) in acetonitrile for up to 60 min.Aluminum contacts (100 nm thick, 1.96 mm² area) were deposited on top ofthis film by thermal evaporation at ˜1e⁵ Torr. The complete devices weresubsequently exposed to a high-humidity air atmosphere at 35 C for up to12 hours to accelerate oxidation of the CQD film. CQD film depositionwas carried out in an inert environment, while BDT treatment andsubsequent handling was performed under ambient conditions.

Means of characterizing photoresponse are now discussed. Devices wereilluminated through the glass substrate and ITO transparent contact.Uniform illumination was provided by a Roithner Lasertechnik 1550 nm LEDarray with an Agilent 33220A 20 MHz function generator used to supply aconstant or modulated bias to the LEDs. The irradiance was calibratedusing a Newport 2930C power meter and 918-IG calibrated photodetectorplaced at the position of the CQD photodiode. Steady-state current wasmeasured with a Keithley 6430 sub-femptoamp SourceMeter and transientcurrents were measured with a Stanford Research SR570 low noise currentpreamplifier and a Tektronixs TDS 220 or TDS 5104 digital oscilloscope.Biases, if used, were supplied by the SourceMeter or currentpreamplifier. Frequency, wavelength, and illumination dependencies ofthe photocurrent were measured with a Stanford Research SR830 lock-inamplifier in current measurement mode. All measurements were performedin a dark, shielded enclosure at room temperature (295 K) in air, exceptfor the temperature-controlled measurements which where measured in anN₂ atmosphere using a bath cryostat. Monochromatic illumination wasprovided by a Jobin Yvon Triax 320 monochrometer with a ScienceTechTH-PS white light source. Multimode optical fibers were used to directthe light to a collimator and the CQD photodiode. Incident irradiancewas invariant within 4% from 400 to 1800 nm. The light was mechanicallychopped at 100 Hz and the photocurrent response at zero bias wasrecorded with a Stanford Research SR830 lock-in amplifier. The spectralphotocurrent was scaled to match the monochromatic response measured at1550 nm. All measurements were performed in a dark, shielded enclosureat room temperature.

Noise measurements are now discussed. Noise was measured in the dark, atzero bias, using a Stanford Research SR830 Lock-in Amplifier in currentmeasurement mode. Noise current was measured directly using the lock-inamplifier and normalized by the input bandwidth. All measurements wereperformed in a dark, shielded enclosure at room temperature (295 K) inair, except for the temperature-controlled measurements which wheremeasured in an N₂ atmosphere using a bath cryostat.

Current-voltage characteristics are now discussed. FIG. 57 shows thesteady-state current-voltage (I-V) characteristics of the CQD photodiodein the dark and at 17.9 μW.cm⁻² illumination at 1550 nm. The darkcurrent characteristics are well described by a diffusion theory ofemission over a potential barrier.¹ The dark current density is 0.1nA.cm⁻² at zero bias and 2.0 μA.cm⁻² at −1.0 V bias. The zero bias shuntresistance of the photodiode (Ro) is determined from the dark current atbiases of +/−0.02 V. Under illumination, a photocurrent is generated, inthe direction opposite to the forward current of the diode, similar toconventional semiconductor diodes. The magnitude of the photocurrent isproportional to the reverse bias, resulting in a dependency of EQE onbias, as shown in FIG. 58.

Characterization of absorption is now discussed. FIG. 59 shows netabsorption in the CQD film as a function of wavelength, calculated fromdirect a direct measurement of total light absorption in the CQDphotodiode structure. The photodiode was placed in an integrating sphereand illuminated directly using a calibrated source. All light reflectedback by the various dielectric interfaces or the Al back contact wascaptured by the integrating sphere, yielding the net absorption of thecomplete device structure. By measuring, separately, the absorption ofthe complete photodiode, the glass/ITO substrate, and an isolated Alcontact, the net absorption in the CQD film was calculated. Allmeasurements were performed with a Varian CARY 500 UV-Vis-NIRspectrometer using an integrating sphere accessory module. Reflectionmode was used for all measurements and both spectral and diffusereflections were collected from the sample.

Temperature dependence of photodiode performance is now discussed.Photocurrent, current noise, and I-V characteristics were measured as afunction of temperature to investigate performance improvements withdecreasing temperature and the dependence of the noise current on RoA.FIG. 60 (a) shows EQE at 1450 nm as a function of temperature. EQEincreases with decreasing temperature as a result of decreased thermalcarrier concentrations and decreased recombination rate at reducedtemperatures. FIG. 60 (b) shows RoA as function of temperature: 1.5e5Ω.cm² at 295 increasing to 8.6e6 Ω.cm² at 235 K. RoA increases withtemperature due to decreased thermal emission of carriers over theSchottky barrier at the Al/PbS CQD junction.¹ FIG. 60 (c) shows measuredi_(noise) and the thermal current noise limit as a function oftemperature. In the absence of illumination or applied bias, noise inphotodiodes originates entirely from thermal noise,^(2,3) and can becalculated, i_(n)=√{square root over (4 k_(b) T/R_(o))}, based on theeffective shunt resistance of the photodiode at zero bias (R_(o)),Boltzman's constant (k_(b)), and the temperature (T). The measuredcurrent noise follows the thermal limit with decreasing temperature, butat magnitudes up to ˜2 fA.Hz^(−0.5) greater. This excess noise may beattributed to a net dark current resulting from a small voltageoverburden in the measurement equipment or environmental noise. FIG. 60(d) shows normalized detectivity (D*) as a function of operatingtemperature. D* was calculated at 1450 nm, the first CQD excitonicfeature, and 1120 nm, the CQD photocurrent response maximum wavelength.D* shows a linear dependence on temperature and is greater than 1e12Jones at 1120 nm for temperatures below 280K, and greater than 1e12Jones at 1450 nm for temperatures below 255K. Although measured using acryostat, these temperatures are readily obtainable using low-costsolid-state cooling.

Depletion depth studies are now discussed. Capacitance measurements as afunction of CQD photodiode bias were used to determine built-inpotential and fixed charge density from a fit to the capacitance-voltagerelationship based on the abrupt junction approximation. FIG. 61 showsthe fit of measured capacitance values to the abrupt junctioncapacitance, revealing a built-in potential of 0.20 V, and a fixedcharge (acceptor) density of 5.0e15 cm⁻³. FIG. 62 shows the depletionregion width calculated from the measured capacitance, using a relativedielectric permittivity of 19.2 (measured using the CELIV technique—seesection 5.0 for details), and assuming a one-dimensional electric fielddistribution. The depletion width at zero bias is calculated to be 240nm. Capacitance measurements were performed using an Agilent 4284A LCRmeter with a 10 mV probe signal modulated at 20 Hz.

Measurement of carrier lifetime is now discussed. Carrier lifetime inthe CQD film was calculated from the open circuit voltage (V_(oc))transient response of the of the CQD photodiode as a function ofirradiance. Under low-injection conditions, the carrier lifetime isinversely proportional to the rate of change of V_(oc), allowing directcalculation from measured V_(oc) transients.⁴ FIG. 63 shows carrierlifetime as a function of irradiance at 1550 nm.

Charge carrier drift mobility was measured directly in the CQDphotodiode structure using the Carrier Extraction by Linear IncreasingVoltage (CELIV) technique.⁵ Under rapid, linearly increasing reversebias, the transient drift current of thermal equilibrium carriersextracted from the quasi-neutral region of a diode can be measuredseparately from the steady-state displacement current. A geometricrelationship, based on the thickness of the semiconductor film, allowsdetermination of the drift mobility from the arrival time of thetransient current maximum. For semiconductors with low thermalequilibrium carrier concentrations, steady-state illumination of thesemiconductor can be used to increase the steady-state carrierconcentration.⁵ The carrier generation rate in the semiconductor shouldbe uniform, but if it not, this technique can be used to identify thepolarity of the extracted carriers. Short wavelength illumination willgenerate more carriers closer to the illuminated surface of thesemiconductor. Reduction of the time required to reach the transientcurrent maximum indicates that the extracted carriers are generatedcloser to the illuminated contact of the device. For the case of the CQDphotodiode, this corresponds to the ITO contact where holes areextracted under reverse bias. Thus confirming that CELIV is measuringthe hole drift mobility—the majority carrier in p-type PbS CQDs.Measurements of optimally BDT treated and air annealed CQD photodiodesreveal a hole drift mobility of 1e-4 cm².V⁻¹.s⁻¹.

FIG. 64 summarizes measured CQD parameters and the values used in themodel presented.

Alternative embodiments of sensitive, fast, smooth-morphologyphotoconductive photodetectors are now presented.

FIGS. 67-69 illustrate an embodiment including smooth-morphologyultrasensitive solution-processed photoconductors.

Solution-processed optoelectronic materials offer a route to low-cost,large-area solar cells, sensors, and integrated optical sources. Whilemuch progress has been made in organic and polymer spin-castoptoelectronics, colloidal quantum dots offer a distinct furtheradvantage: convenient tuning of bandgap, and thus absorption onset, viathe quantum size effect. Such tunability is relevant to diverseapplications such as multispectral image sensors, high-efficiencymultijunction solar cells, and multicolor and white light sources.Ultrasensitive photoconductive photodetectors have recently beenreported, both in the visible and infrared, based on size-effect tunedcolloidal quantum dots. These first reports relied on the removal orexchange of organic ligands that resulted in rough films incompatiblewith the realization of high-uniformity image sensors. In general suchsolid-state exchanges have shown great promise in enhancing electronictransport in colloidal quantum dot films, but have consistently beenreported to generate cracking ascribed to their loss of volume duringthe exchange. Here we report a new route to high-performancephotoconductive photodetectors, one that results in sub-1% roughness, ascompared to >15% for past solid-state exchanged devices. The devicesreported herein provide photoconductive gains evidenced in their typical7 A/W responsivities. This new method reveals an added significantadvantage: the devices respond with a single time constant of 20milliseconds, compared to the multi-second and multi-time constantresponse of previously-reported devices. Single-time-constant temporalresponse below 100 ms is crucial to video-frame-rate imagingapplications. Top surface photodetectors made using novel materialsoffer access to spectral regions unseen by fixed-bandgap silicon. Threecrucial attributes must be exhibited by any top-surface detectortechnology intended for applications in imaging: sensitivity, spatialuniformity, and speed of response. Sensitivity may be described by thenoise-equivalent power (NEP)—the lowest light level that can bedistinguished from noise. D*, the normalized detectivity, enablescomparison among pixels having different areas. Uniformity of gain anddark current across a pixel array are required to avoid the introductionof spatial noise into an image: photoresponse nonuniformity of less than1% is required, mandating film thickness nonuniformity (TNU) of thissame order. Finally, temporal response must be sufficiently rapid as toenable video frame-rate imaging. At a minimum, sub-100 ms time constantsare required. Photoconductive photodetectors based on solution-processedcolloidal quantum dots have, to date, exhibited remarkablesensitivities, with D* reaching into the 10^12 and even 10^13 Jones,comparable to that achieved by the best epitaxially-grownphotodetectors.

Large photoconductive gains, as high as thousands of electrons collectedper photon incident, have played a key role in achieving thissensitivity. These high gains relied on enhanced conduction in filmsachieved by applying further processing to already-cast films consistingof quantum dots passivated with insulating organic ligands. Ligandremoval, ligand replacement, and film crosslinking all produce thedesired increase in mobility that lead to increased sensitivity; but areaccompanied by a significant loss of film volume. This film contractioncauses these processes to lead to film cracking—often on multiplelengthscales ranging from nanometers to micrometers—that renders theresultant films unacceptable for applications that demand exceptionallyuniform films.

Realization of useful levels of photoconductive gain and excellentmorphology are not incommensurable. Relying on processes that producelarge changes in film volume may complicate realization of excellentmorphology. After they have been synthesized, colloidal nanoparticlesare capped with long, insulating organic ligands. These serve a numberof purposes. During synthesis, they bind the metal precursor—in ourcase, lead-oleate brings the metal to the reaction. Once the synthesisis complete, ligands remain on the surface, preventing aggregation andkeeping the nanoparticles dispersible within a nonpolar solvent. Theligands also serve to passivate dangling bonds on the nanoparticlesurface. While oleate ligands are very effective at preventingaggregation, one side effect of the use of long aliphatic chains is thata colloidal quantum dot solid made from such materials is highlyinsulating. A procedure that exchanges original ligands with shorterligands is needed if electron and hole transport among the nanoparticlesis to occur with reasonable efficiency. Recent work on photoconductivephotodetectors reveal that such an exchange is indeed necessary to bringmobilities into the >1E 4 cm2/Vs regime needed to ensure that transitacross the device occurs much more rapidly than combination. This is theprerequisite for photoconductive gain. However, these past works allemployed solid-state treatments that led to poor morphology to achievetheir high gains.

Ligand exchange implemented instead within the solution phase may becontemplated. Good transport requires extremely short ligands; butsolution-phase exchange to such short ligands typically results inconsiderable nanoparticle aggregation. In this case, morphology is onceagain compromised, and excitonic features and thus size-effecttenability are lost. An approach to solving the aggregation problem isto avoid the use of weakly-bound ligands are used, such as amines; theselabile ligands create many opportunities for irreversible aggregationduring the course of the solution-phase exchange. Mercaptans, whosethiol group binds very strongly with Pb, may be exchanged onto thesurface of PbS nanocrystals. Embodiments include beginning witholeate-capped PbS nanoparticles having a first excitonic feature at 950nm, that were dispersed in toluene. We added to them an equal volume ofethanethiol. Embodiments include allowing the mixture to incubate fortimes ranging from 15 minutes to multiple hours. Ligands exchange may beterminated by precipitating the colloid using hexanes. Purelyoleate-capped PbS nanoparticles are stable in n hexanes as well as intoluene; the effectiveness of this non-polar solvent in precipitatingthe exchanged nanoparticles suggests that the nanoparticle surfacedemonstrated a more polar character owing to the shorter ligands. Wepelleted the colloid via centrifugation and resuspended the nanocrystalsin chloroform. We constructed devices by spin-coating the exchangedmaterials onto planar glass test chips patterned with goldinterdigitated electrodes. Having created a simple process thatgenerates stable solutions of short-ligandcapped nanoparticles, wesought to investigate its impact on colloidal quantum dot filmmorphology, responsivity to light, and temporal response.

Atomic force microscopy and profilometry may be used to study thesurface morphology and film thickness. We investigated: (a) Films madefrom unexchanged nanocrystals; (b) Films made by spin-castingunexchanged nanocrystals and subsequently treated with butylamine; (c)Films made by spin-casting nanocrystals previously exchanged tobutylamine in the solution phase; (d) Films made by spin-castingnanocrystals previously exchanged to ethanethiol in the solution phase.We present in FIG. 67 the comparison of the results. Films made fromunexchanged nanocrystals exhibit large regions of extensive crackingupon drying; their roughness is 25% of their thickness. When such filmswere subsequently treated with butylamine they continued to show cracksbut their roughness was somewhat reduced to 9% of their thickness. Filmsmade from nanoparticles exchanged to butylamine in the solution phaseexhibited 15% roughness. In striking contrast, films made byspin-coating ethanethiol-exchanged quantum dots produced 0.6% roughness.Films of slightly over 200 nm thick are thickness for photodetectorrealization in view of the substantially complete absorption of visiblelight in films of this thickness.

Volume contraction readily explains the poor morphology of the oleatecapped particle film treated from the solid state using butylamine. Wesought to understand further why solution-exchange to butylamine alsofails to produce good-morphology films. We compare in FIG. 68transmission electron micrographs for original nanoparticles,butylamine-solution-exchanged nanoparticles, and ethanethiol-exchangednanoparticles. The butylamine-solution-exchanged nanoparticles haveaggregated considerably, some of them forming worm-like structures, withclusters of nanoparticles as large as 50-100 nm. In contrast, theethanethiol-exchanged nanoparticles remain discrete and monodisperseddots. Comparison of oleate-capped with ethanethiol-exchangednanoparticles reveals much closer interparticle spacing in theethanethiol-exchanged case.

We anticipated that the extent of aggregation inbutylamine-solution-exchanged particles would also be manifest in theirabsorption spectrum. A complete loss of excitonic structure is indeedrevealed in FIG. 68 (a). In stark contrast, the ethanethiol cappednanoparticles preserve the sharp feature of the as-synthesizedparticles. Because the ethanethiol-exchanged films were opticallysmooth, we were able to use interference features in their absorptionspectra to estimate their refractive index. We obtained a value of 2.38,compared with previous reports of 1.64 in oleic-acidcapped nanoparticlefilms. This finding is consistent with the considerably closer packingseen in the TEM images.

We now turn to the characterization of these devices as photoconductivephotodetectors. At a bias of 10 volts across our 5 μm-wide lateralelectrode gap the oleate-capped nanoparticles exhibited a dark currentof less than 1 pA for an electrode width of 3 millimeters and nophotoresponse. All three treatments result in orders of magnitude higherdark current. The photoconductive gain of the solid-state treateddevices is in a practically useful regime (order 10), whereasbutylamine-solution-exchange nanoparticles show gain of 150, likely toresult in excessive photocurrent and presenting challenges in imagingapplications requiring local integration of the photosignal within afinite-sized capacitor. Most striking is the difference in temporalresponse among the different photodetectors. Both butylamine treatmentslead to multi-temporal-component responses that include a significantslow tail of response on the timescale of seconds. In contrast,ethanethiol-solution-exchanged devices exhibit a single 20 millisecondtime constant. We show this temporal response in FIG. 69.

Thus, while photoconductive photodetectors do exploit trap states toachieve gain, it is possible to engineer the combination of transportand trap lifetime to achieve a compelling combination of gain andtemporal response. Indeed the long-lived temporal response of thebutylamine-treated film provides no advantage in gain over itsethanethiol-exchanged counterpart in exchange for its highly undesiredlong-tailed transient.

Experimental First, a mixture of PbO (0.9 g, 4.0 mmol), of oleic acid(2.67 g, 9.5 mmol), and of octadecene (4.73 g, 18.8 mmol) are degassedin nitrogen at 95° C. for 16 Hours, and labeled solution A. Next,hexamethyldisilathiane (210 μL) is mixed with octadecene (10 mL) in anitrogen glove box and labeled solution B. Then, solution A (19.5 mL) isinjected into a flask, under nitrogen, and the temperature of thesolution is raised to 120° C., using a heating mantle, under heavystirring. Solution B is then injected into the flask. After theinjection, the heat mass of the heating mantle is used to slowly coolthe reaction flask. When the temperature reaches □35° C. quench thereaction with distilled Acetone (40 mL). Wash with multiple suspensionsin toluene and precipitations in Acetone while keeping only suspendedphases. Film formation: films were formed by spin coating a ethanethiolexchanged solution

(65 μL) of PbS nanocrystals at 700 rpm onto gold interdigitatedelectrodes on a glass

chip that was previously, repeatedly, washed in acetone and water andthen dried under

nitrogen. A profilometer was used to measure PbS nanocrystal filmthicknesses ranging from 213 nm for ethanethiol-solution-exchange, 712nm for butylamine treated films, 1978 nm forbutylamine-solution-exchange, and 429 nm for oleic acid unexchangedfilms. Absorption spectra were collected using a Cary model 500spectrophotometer to characterize film excitonic features, and to studythe Fabry-Perot effect of glassy ethanethiol solution exchanged PbSnanocrystal films. Electron microscopy images were acquired using thescattered-electron detectors of a Hitachi HD-2000 scanning transmissionelectron microscope operating at 200 kV.

Example Systems and Applications of Embodiments

In an embodiment, low-cost, large-area solar cells may offer theprospect of economically-sustainable clean energy capture. The bestsolid-state solution-processed solar cells have to date produced powerconversion efficiencies in the range of 3-5%. One factor limiting theirfurther improvement is solution-processed photovoltaics' transparency tothe sun's infrared rays. Half of the sun's power reaching the earth liesbeyond 700 nm, and one third beyond 1000 nm. However, the best reportedinorganic thin-film nanocrystal-based devices absorb only to the blue of800 nm, and organic polymer/C₇₀-derivative devices are effective out toabout 1000 nm, with their peak efficiency lying at 800 nm.

For these reasons, there is a need to realize solution-processedshort-wavelength infrared (SWIR) photovoltaic devices. In 2005 it wasreported that spin-coated colloidal quantum dots, combined with apolymer matrix, produced a photovoltaic effect. However, these blenddevices exhibited external quantum efficiencies less than 0.006% at 975nm. Further development of bilayer devices has so far improved externalquantum efficiencies to 0.4% at 975 nm.

Nearly a two-order-of-magnitude increase in the external quantumefficiency of solution-processed SWIR photovoltaics can be realizedrelative to previous reports. The approach described herein is supportedby two recent findings in the electronic properties ofsolution-processed quantum dot films. First, it was recently shown thatfilms of pure quantum dots—with no heterostructure matrix, and withinsulating organic ligands modified or removed—can exhibit mobilitiesgreater than 0.1 cm²/Vs. Second, since the previous record exhibitedtransport-limited external quantum efficiencies, it was determined thata rough-interface architecture that increased absorbance while keepingexciton-separation efficiency high would be required.

A bottom (non-optically-absorbing) electron-accepting electrodehigh-surface-area nanoparticle ITO may be used. Solution-processablehigh-surface-area materials capable of forming a Type II heterojunctionsuitable for charge separation include ZnO, SnO₂, and ITO. The inset ofFIG. 3 r shows the expected Type-II energy band diagram formed betweenPbS and ITO. This material was selected to obtain conductivities up to 5orders of magnitude higher than using ZnO or SnO₂.

PbS nanocrystals was synthesized using an organometallic routepreviously described. As-synthesized, the nanocrystals are capped with˜2.5 nm long oleic acid ligands. These impede charge transport,producing insulating thin films. To create conductive nanocrystalsfilms, a solution-phase ligand exchange was used to replace oleateligands with ˜0.6 nm long butylamine ligands. Following ligand exchange,the butylamine capped nanocrystals exhibited linear I-V characteristics.

The ITO phase of the bulk heterojunction was fabricated by spin coatingITO particles, originally suspended in water, onto a glass substrate.The film was then baked in air at 310° C. for 30 minutes resulting in 3μm thick films with resistivities on the order of 0.5 ohm*cm. FIG. 3 oaand FIG. 3 ob show the resulting high surface area film.

Devices were fabricated by soaking the ITO-coated substrate in a 5 mg/mlsolution of butylamine-capped PbS quantum dots in chloroform for 10minutes. An absorption spectrum of the device shows a nanocrystalspectral absorption characteristic indicating that the nanocrystals haveindeed deposited. Subsequent deposition iterations were employed untilsaturation was observed in the growth of the nanocrystal absorptionfeature. Magnesium contacts capped by a layer of silver were thendeposited via thermal evaporation; however, all of the devicesfabricated using this method were found to result in short circuits whencurrent-voltage (IV) curves were taken.

FIG. 3 oc shows an area of the ITO-PbS quantum dot device before metalcontacts were evaporated. The exposed bare ITO in the device led todirect contact with the deposited metal. FIG. 3 od shows a highermagnification image of the exposed bare ITO. Here individual PbSnanoparticles can be seen clustered in the crevices formed betweensintered ITO particles.

In identifying a technique to guarantee complete coverage of the rough,spiky ITO by the PbS quantum dot layer, a linker molecule,mercaptoacetic acid, that at one end attached to the ITO via acarboxylic group, and at the other end attached to PbS via a thiolgroup, could lead to complete coverage. Bifunctional linker molecules ofthis type are used for the attachment of monolayers of visible-sensitivequantum dots as sensitizers in metal oxide/liquid electrolytephotovoltaic cells. This method, too, led to short circuits due to aninability of this method to create a smooth, continuous film atop therough shards emanating from the underlying nanoporous ITO electrode.

Techniques were sought in which the PbS quantum dots were not directlylinked to the ITO; but instead to link PbS nanoparticles to one another.This could lead to lateral growth of the PbS film in such a way as toovergrow the faceted shards of ITO. This approach involved the use of abridging molecule to facilitate interparticle-linking. Although bridgingmolecules have been used for monolayer deposition of semiconductornanoparticles on metal electrodes, they were used instead herein todirect multilayer particle assembly in both lateral and verticaldirections towards the realization of a planarized film on a roughsubstrate. Ethanedithiol was selected for two reasons. First, thiolspossess a strong affinity for Pb atoms, leading to effective competitionwith the existing amines for ligand-binding sites. Second, ethanedithiolis short (˜0.7 nm) enough that any thiols remaining after subsequentdevice processing would not significantly impede charge transport. Dueto dual role of the quantum dots as both radiation 1000 absorber andhole transport medium our use of a cross-linker molecule additionallycoincided with a desire to improve electrical transport properties.Previously the charge transport mobility in thin film transistors andconducting nanoparticle solids has benefited by the use of hydrazine and1,4 phenylenediamine as cross-linking molecules.

Devices of an embodiment were fabricated using this cross-linkerstrategy by treating ITO in a 1% by volume solution of ethanedithiol inacetonitrile for 30 min. The ITO was then soaked in a nanocrystalsolution for 10 min. This procedure was repeated three times. As seen inFIG. 3 oe and FIG. 3 of, this produced smooth, continuous films. It wasfound that once top metal contacts had been deposited these devicesproduced short-free IV characteristics.

A way was sought to demonstrate the value of quantum-size-effect tuningof quantum dot absorption onset by constructing classes of deviceshaving two different excitonic spectral locations. One nanocrystal batchwas selected with a first excitonic transition at 1340 nm; and for thelonger-wavelength device, at 1590 nm. As-fabricated, devices illuminatedunder monochromatic 975 nm illumination exhibited short-circuit externalquantum efficiencies of 2.3% in the 1340 nm device and 0.3% in the 1590nm nanocrystal device, in both cases with illumination intensities of 12mW/cm².

Thermal treatment of the devices of an embodiment could offer thepotential to improve transport within the quantum dot film, as well ascharge separation across the quantum dot—ITO interface. Devices sinteredin air for 3 hours increased to 9% EQE at 975 nm (1340 nm devices) and16% EQE (1590 nm devices). FIG. 3 p shows a table summarizing theeffects of sintering on the performance of the devices.

Current-voltage traces were provided for the 1340 nm device in FIG. 3 q.Data taken under 100 mW/cm² AM 1.5 illumination was included using anOriel solar simulator. These devices showed AM 1.5 power conversionefficiencies of 0.5%. Monochromatic power conversion efficiencies at 975nm were 1.25% for 12 mW/cm² illumination and 0.95% for 70 mW/cm²illumination.

Illuminating the devices with monochromatic light and measuring thecurrent generated under short circuit photovoltaic operation measuredthe external quantum efficiency of the devices. The plot in FIG. 3 rshows the spectrally-resolved external quantum efficiency which revealsa photoresponse extending to more than 1700 nm in the device fabricatedwith 1590 nm first exciton transition nanocrystals. The spectral EQE fordevices composed of both sizes of nanocrystals follows closely theirrespective absorption spectra. A peak EQE of 46% occurred at 500 nm inthe sintered 1590 nm device while the sintered 1340 nm device exhibiteda peak EQE of 15% at 590 nm. The decrease seen in EQE below about 500 nmis due primarily to increasing absorption in the ITO.

Devices fabricated in the manner described herein were subsequently leftunder ambient conditions in an open circuit configuration forapproximately seven months. After this time it was observed that the topdeposited contacts had oxidized, significantly degrading deviceperformance. Once new contacts were deposited, however, the devicescontinued to function with photovoltaic efficiencies only slightlydegraded from that obtained seven months earlier.

In embodiments, the QDPC 100 may be a part of an integrated system 2200,including structures 2202 and features 2204, that is utilized inapplications and markets 2100, such as cameras 2102, sensors 2104,visible sensors 2108, IR/UV/X-Ray sensors 2110, multi-spectral sensors2112, high gain imagers 2114, memory 2118 applications, commercialmarkets 2120, consumer markets 2122, medical markets 2124, civil markets2128, military markets 2130, machine vision markets 2132, sensor markets2134, and the like. In embodiments, the integration of the QDPC 100 withproducts and systems may provide improved performance, reduced cost, andinnovative products that are applicable to new market segments.

The QDPC 100 may utilize a plurality of functional platform structures2202, features 2204, and benefits. In embodiments, these features 2204and benefits may be enabled through a set of properties for thecolloidal quantum dots used in the detectors, such as no phasetransitions between minus 40 to 350 degrees C., amenable to colloidalsynthesis, simple etch chemistry, exciton radius such as to facilitatequantum-size effect tuning (2-20 nanometers), environmentally friendlymaterials, continuum band edge beyond 1.5 microns, no melting,controlled trap states through a facile means, long lifetime states (1millisecond to 1 microsecond), transit time/mobility in a solid phase,no degradation in UV/VIS/IR exposure, no reaction with oxygen or waterunder relevant operating or processing conditions, no reaction withinternal metals, thermal expansion coefficient matched to typicalelectronic materials, multi-spectral, broader placement options, smallchips (lateral) thin chips, and the like.

In embodiments, these features 2204 and benefits may be enabled througha set of characteristics, such as the ability to use varioussub-combinations of IR/X-Rays/UV/VIS 2108 2110 bands, self-poweringusing modulated IR 2110 source to harness spectral absorption, arraysize, chip size, detecting radiation 1000 with high responsively,tunable to different wavelengths, low noise, noise reduction, ease tomanufacture, high sensitivity, high gain, and the like. Very highsensitivity of the QDPC 100 may allow for much faster stabilizationtime, high field-stop number and small aperture lens to give improveddepth of field, no need for a flash, and the like. No need for a flashwith the QDPC 100 may enable improved capabilities, such as picturesthat are more pleasing because there is no need to use a flash, flashreflections are eliminated, natural radiation 1000 may be morefrequently used, run exposure faster to eliminate camera 2102 shake,better action shots with the higher speed, long distance shots becauseof no shake, interactive video game applications, high-speed cameras2102 for watching 2D or 3D motion (up to 120 frames per second).

In embodiments, the QDPC 100 may be able to store information in a framebuffer 2118 or memory 2118, read out or from memory, or write back intomemory 2118. The ability to store information within a quantum dot pixel1800 may enable a plurality of functions, such as having a frame buffer2118 behind each quantum dot pixel 1800, multiple frames behind eachquantum dot pixel 1800, compression engines for video, imagemanipulation, vector for guiding mpeg-based compression engines,processing to find something going across the image, or the like. Theability to write data back into the quantum dot pixel 1800 may enable aplurality of functions, such as using the frame buffer 2118 for storage,manipulation of the data in the buffer, providing flash memory 2118behind each quantum dot pixel 1800 to note or detect dead quantum dotpixels 1800, user storage, store compressed multiple frames in buffer2118 where a user views all and selects the best, execute an imagerotation, use for high-rate video compression, provide a function forimage stabilization, increase shot-to-shot speed with multiple shotsstored into memory 2118, provide spatial Fourier transform right on thechip 2000, running an automatic exposure or automatic focus enginefaster because of QDPCs 100 high gain 2114.

The ability to store information in quantum dot pixels 1800 mayeliminate the need for exposure control. In embodiments, every quantumdot pixel 1800 could report exposure within a very large range. Valuesmay be assigned, say with one indicating very bright radiation 1000 andthe other indicating very low radiation 1000. The two may be convertedwith an analog-to-digital converter, and then combined. One responds tobias, the other is the value of photocurrent at that bias—same exposureon one quantum dot pixel 1800. One value is associated with the biasvalue and the other with how much current was collected at the biasvalue, where the bias is the gain set and the course information isassociated with the intensity. The process may take the form of logcompression, where the value is shifted around the center point of thedynamic range. In embodiments, having automatic gain control on eachpixel, as opposed to across the entire quantum dot pixel 1800 array, mayeliminate exposure control. In embodiments, there may be no need forexposure control or for auto-focus, which may provide an instant-actingcamera 2102.

In embodiments, there may be automated gain 2114 control in a quantumdot pixel 1800, providing a pixel-by-quantum dot pixel 1800 localcontrast that does not require a buffer 2118. It may be possible toachieve high dynamic range without any processing, with in-pixelauto-gain 2114 control. Gain level 2114 may be self-selected with theaddition of pixel circuitry 1700. In a cluster of four pixels 1800,automatic gain 2114 control could be performed in a Bayer pattern group,where a shared bias pixel 1800 is at the center of the two-by-twoquantum dot pixel 1800 configuration. With this configuration, it may bepossible to report the dynamic range for the group, as opposed to forevery quantum dot pixel 1800. In addition, with good post-processing,interpolation may be used to adjust the gain 2114 level. In embodiments,a self-selecting automatic gain 2114 level may be implemented, where theexposure is always set as fast as it can be while maintaining imagequality. In this instance the auto-gain 2114 system may be associatedwith the exposure system. The system may provide for fast auto-exposureand auto-gain algorithms, which utilize the histogram and time historyof the image using the frame buffer 2118. This may allow auto-gain 2114and auto-exposure to look at histogram from an array of pixels 1800(plus more) that gives radiation 1000 levels and a range of where thequantum dot pixel 1800 level is, in order to choose the best exposuresetting.

In embodiments, an IR 2110 laser may be utilized to help eliminatecamera 2102 shake, for example by taking an number of pictures in aquick sequence and averaging them to remove the shake. The IR 2110 lasermay be used as the vector, and wouldn't show up in the visible 2108picture. This may apply to a military application 2130, where shake isoften an issue. Consumer products may only look at something with over acertain number of shakes, say over a limited number of quantum dotpixels 1800, and subtract the shake out. In embodiments there may bemore blur at the edges due to lens effects, and so boarder pixels may beused to subtract out.

Anti-shake techniques may also be applied to taking video, whereprocessing must be done in real-time. Video anti-shaking may requiretracking how much shaking is taking place, and then to shift coordinatesof the image in quantum dot pixel 1800 memory. Determining how muchshaking is taking place may also require performing a correlationcalculation. The technique may take advantage of the fact that videocameras 2102 typically already have IR 2110 range finders, laser rangefinder, or the like, to utilize in the process.

Range finding may be possible through measuring the time-of-flight of alaser out and back to the pixel 1800. In an embodiment, there could be avisible 2108 quantum dot pixel 1800 array overlaying one IR 2110 quantumdot pixel 1800 for range finding or time gating. The visible 2108 and IR2110 could then be mixed and manipulated to determine the range, from IR2110 and visible 2108 together, and the image, from the visible 2108quantum dot pixel 1800 array. With the use of stacked pixels 1800, therecan be a color layer on top and the IR 2110 layer below it. The IR 2110may pass through the visible 2108 layer and absorbed in the IR 2110layer, without effecting the visible 2108 layer image. A single layerRGB-IR may also be able to be used.

In embodiments, sensors 2104 may be made very thin, especiallyapplicable to the commercial 2120 mobile phone market where thethickness of the display and camera may largely determine the thicknessof the phone. Users always want higher resolutions, and higherresolutions may translate into bigger sensors 2104, which in turn maycall for a taller lens, and this may drive cost up. Thin sensors 2104may be better enabled because of a very steep angle relative to thesensor 2104, enabled by the quantum dot material 200. Low radiation 1000sensors 2104 may also be enabled through the increased sensitivity ofthe QDPC 100 technology, may enable pictures with no flash, ambient andlow radiation 1000 photography, low radiation 1000 monitoring camera forsecurity, hand-shake reduction, and the like. In embodiments, the QDPC100 technology's greater sensitivity to low radiation 1000 applications,and large chief angle and low refractive index for the development ofthin sensors 2104, may provide for improved and innovative applicationsfor new sensors 2104.

In embodiments, QDPC 100 sensors 2104 may be applied to theshort-wavelength infrared (SWIR) (1-2 um) spectral regions, wherereal-time medical imaging in the low-autofluorescence tissuetransparency windows are centered at 1100 and 1350 nm [6], enablingreal-time guidance of surgeons leading to complete resection of lymphnodes in an animal model [7]. The transparency of pigments and ofsilicon wafers may make the SWIR critical to machine vision inspection,and the 1-2 um region contains up to seven times more optical power on amoonless than any other spectral band, enabling un-illuminated nightvision [8].

In embodiments, the QDPC 100 may be applied to commercial markets 2120such as laptops, cell phones, cameras 2102, wireless cameras, USBcameras 2102, scanners, pointers, video conferencing, and the like. Forinstance, a low radiation 1000 and multi-spectral 2112 application of aQDPC 100 cell phone may enable a user greater security by viewing darkplaces like an alley at night. Cameras 2102 can be no-flash night shotcameras 2102, or externally powered by a laser, multi-spectral 2112,self-configuring, and the like. Scanners may be used for fingerprinting,array scanners for film negatives or documents, read-write head scannersfor DVD/Blu-Ray, and the like. QDPC 100 enabled pointers may replace 2Dgyro enabled pointers by utilizing a mapping of objects of reference inthe visual field or using GPS plus objects, camera-based addressingsystems for lighting networks, GPS associated with imaging systems,delocalized collaborative mode where a user could make use while mobileat a desk (browse through the Eiffel tower), and the like. Cell phoneenabled QDPC 100 may take advantage of the very thin nature of the QDPC100 technology to create thinner phones.

In embodiments, the QDPC 100 may be applied to the consumer market 2122,such as applied to gaming, 2D and 3D positional imaging, edge detection,motion tracking, green screen effects, peer-to-peer communications,multi-spectral effects, eye tracking and pupil position tracking,wearable cameras 2102, dark room vision with reduced color, game stationwith camera 2102, and the like.

In embodiments, the QDPC 100 may be applied to the medical market 2124,such as with multi-spectral imagers 2112, X-ray imagers 2110, wearableX-Ray 2110, assaying systems, endoscopy, scopes, pill cameras 2102,bloodstream cameras 2102, disposable micro-cameras 2102, eye-trackingsystems, pupil monitoring, diagnostics, machine vision 2132 processingsystems, wearable cameras 2102 for tracking patient behavior, and thelike.

In embodiments, the QDPC 100 may be applied to the civil market 2128,such as retinal scanning from a distance, facial recognition, homesecurity, personal security, child and elderly monitoring, ambientradiation 1000 insensitive security applications with modulated IR 2110and IR 2110 combined with multi-spectral 2112 color security camera2102, ATM machine cameras 2102, store monitoring cameras 2102, and thelike.

In embodiments, the QDPC 100 may be applied to the military market 2130,such as with night-vision cameras 2102, no-shake cameras 2102,low-radiation 1000 cameras 2102 that are black and white in lowradiation 1000 and color in high radiation 1000, night-vision with rangefinding, multi-spectral 2112 cameras 2102, and the like. QDPC 100enabled cameras 2102 may allow the military to view scenes underdifferent conditions with a single camera 2102, such as under day,night, smoke, fog, rain, and the like conditions. These cameras 2102 maybe used by individuals, or mounted on a vehicle to provide all-conditionviewing, such as on an unmanned aerial vehicle (UAV). Multi-spectral2112 viewing systems may be ultra-wideband optical device, viewingacross a wide range of the spectrum, such as simultaneous viewing of IR2110, visible 2108, and UV 2110.

In embodiments, the QDPC 100 may be applied to the machine vision market2132, such as the integration of very small cameras 2102 onto a roboticsarm, multi-spectral 2112 inspection of products, simultaneous image andedge detection during inspection and counting, low-radiation 1000inspection, integrated image processing for control algorithms, highresolution high gain 2114 cameras 2102, pattern recognition anddetection, stored calibration images in memory 2118, and the like.

In embodiments, the QDPC 100 may be applied to the sensor market 2132,such as used in combination with emitters, such as a quantum dot LEDwhere the solution is applied to the top of a semiconductor element andradiation 1000 is emitted through a focusing lens, a camera 2102 thatemits an image as it simultaneously views the scene, a single chipcamera-light, and the like. In embodiments, radiation 1000 emittingquantum dot structures 1100 may be used in combination with existingdetector technologies, such as CMOS and CCD detectors with an emittingdetector surface.

In embodiments, an integrated fingerprint sensor may be implemented bycombining (1) An array of photoconductive regions independent read usinga read-out integrated circuit (2) A source of illumination in thevisible, or in the infrared, or both, that illuminates the subject to beread, and provides a signal for the photoconductive regions of (1) tosense.

In embodiments, the QDPC 100 may provide unique solutions to a pluralityof markets. These unique solutions may be enabled through QDPC 100functional platform features and benefits, as described herein, that mayprovide technological advantages that help to generate productinnovations across a wide range of market applications.

Although the QDs are solution-deposited in the described embodiments,the QDs may deposited in other ways. As mentioned above, one motivationfor using solution-deposition is its ready compatibility with existingCMOS processes. However, satisfactory devices can be made byvacuum-depositing or otherwise depositing the QDs.

Numerous example embodiments follow, including example embodiments of orincluding one or more of the materials, systems, devices and methods,described above and/or within the scope of the teachings presentedherein.

The embodiments described herein include a number of aspects includingan image sensor which includes an optically sensitive detector layerformed on an underlying integrated circuit, patterned to measureradiation impinging upon the detector layer and to provide processingand control associated with the image. Various alternative embodimentsof the image sensors and host devices described herein are not limitedto including the quantum films described herein.

Other aspects of the embodiments associated with the application ofquantum dot films to image sensors include quantum dot processing andligand exchange, quantum dot film formation, puddle casting, ligandexchange during film formation, growth from solution patterning andligand exchange during film formation, patterning, stacked layers of dotmaterial with electrical interconnect to read through a dielectriclayer, etched electrical interconnects, calibrating a signal relating toa received charge from a first layer of quantum dot material,multi-layered quantum dot pixel layout, filterless photodetector,quantum dot pixel chip, embedded pixel circuitry, integrated circuitrywithin the quantum dot pixel chip, and product applications thereof.

In embodiments described herein, post-synthetically processing quantumdots may include precipitating the quantum dots, centrifuging thequantum dots, decanting the supernatant above the quantum dots, dryingthe quantum dots, redispersing the quantum dots in a solvent, filteringthe redispersed quantum dots by size, and the like. Precipitating thequantum dots may involve placing the quantum dots in a solvent selectedfrom the group comprising methanol, acetonitrile, ethyl acetate,isopropanol, propanol, and the like. The solvent for redispersionfacilitates ligand exchange may be selected from a group includingamine-terminated ligands, carboxyl-terminated ligands,phosphine-terminated ligands, polymeric ligands, and the like, where thesolvent for redispersion is one or more of chloroform and butyl amine.

In embodiments described herein, quantum dot film formation may includea substrate for a quantum dot film and depositing a film of quantum dotson the surface of the substrate by at least one of spin coating, puddlecasting, electrodeposition, vapor deposition, air brush spraying, growthfrom solution, hydrophobic systems, acceleration/evaporation in gasphase, photocopying, and ink jet printing. Ligand exchange may also beexchanged by dipping the substrate into a ligand-containing solvent,where the ligand is at least one of benzenedithiol, methanethiol,ethanethiol, and ethanedithi, and the solvent is at least one ofacetonitrile, methanol, and toluene. Electrodeposition may proceed untila photocurrent generated by the quantum dot film being formed reaches athreshold, where air brush spraying may include entrainment of thequantum dots in a solvent. Activating the quantum dot film by one ormore of an air bake and a methanol dip, and disposing an encapsulantover a portion of the quantum dot film, an encapsulant over a portion ofthe substrate, a passivation layer over a portion of the quantum dotfilm, or the like.

In embodiments described herein, forming a quantum dot film may includea substrate for a quantum dot film, depositing a puddle of quantum dotsolution onto the surface of the substrate, causing the quantum dots toprecipitate out of solution and form a quantum dot film on the surfaceof the substrate, and the like. Precipitation may be facilitated by acrosslinker introduced to the puddle or by crosslinker deposited on thesurface of the substrate, where the crosslinker may be one or more ofdithiol, diamine, dicarboxylic acid, ethanedithiol, thioglycolic acid,or the like, and the crosslinker may be deposited in a pattern along thesubstrate. In addition, the precipitation may be facilitated by atemperature change, solvent volatility, pressure applied to the puddle,a duration of time, a gas blown onto the puddle, introduction of anon-solvent to the puddle where the non-solvent may be one or more ofmethanol, ethyl acetate, acetonitrile, propanol, iso-propanol, or thelike. Further, the puddle may be confined to an area on the surface ofthe substrate.

In embodiments described herein, a quantum dot film may be formed byproviding a substrate for a quantum dot film, immersing the substrate ina solution of ligand to form a ligand-coated substrate, dip-coating theligand-coated substrate in a quantum dot solution, causing the quantumdots from solution to aggregate on the surface of the ligand coatedsubstrate, and forming a quantum dot film on the surface of theligand-coated substrate and causing ligand exchange at substantially thesame time.

In embodiments described herein, a quantum dot film may be formed byproviding a substrate for a quantum dot film, attaching a crosslinker tothe surface of the substrate, dipping the substrate with attachedcrosslinker in a quantum dot solution, and causing growth of a quantumdot film at a location on the substrate with attached crosslinker. Thecrosslinker may be one or more of dithiol, diamine, dicarboxylic acid,ethanedithiol, thioglycolic acid, or the like, where the crosslinker isdeposited in a pattern along the substrate. The ligand exchange may becaused by dipping the substrate with disposed quantum dot film into aligand-containing solvent, where the ligand is one or more ofbenzenedithiol, methanethiol, ethanethiol, and ethanedithiol, and thesolvent is one or more of acetonitrile, methanol, and toluene.

In embodiments described herein, patterning a quantum dot film mayinclude providing a substrate for a quantum dot film, causing a patternto be presented on the surface of the substrate, and disposing a quantumdot film on the surface of the patterned substrate. The quantum dot filmmay be disposed substantially along a pattern, where the quantum dotfilm is disposed substantially along a void in the pattern. The film maybe treated to remove portions of the film disposed along the pattern ora void in the pattern, where the pattern may be created by etching thesubstrate. Etching may be one or more of dry etching, chlorine etching,and fluorine etching, where masking creates the pattern. Disposing aquantum dot film may include precipitating the quantum dotssubstantially at the surface of the substrate, activating the quantumdots at the surface of the substrate. The pattern may be created bydepositing crosslinker in a pattern on the surface of the substrate,where the crosslinker may be one or more of dithiol, diamine,dicarboxylic acid, ethanedithiol, thioglycolic acid, or the like.Disposing a quantum dot film may include quantum dot epitaxy, wherequantum dot epitaxy may be analogous to molecular beam epitaxy,metalorganic chemical vapor deposition, chemical beam epitaxy, or thelike.

An image sensor is described herein comprising (1) a substrate (2) ananocrystalline film over a portion of the substrate (3) a substantiallycontinuous layer conformally covering the nanocrystalline film and theexposed portions of the substrate; such that gases, liquids, and solidsdo not permeate the nanocrystalline film.

In embodiments described herein, reading an electrical signal from aquantum dot structure may include providing a multi-layered quantum dotstructure comprising at least two optically stacked quantum dotstructure layers, a first layer and a second layer, separated by adielectric, providing an electrical interconnect that passes through thefirst layer and is electrically associated with the second layer,wherein the electrical interconnect is substantially electricallyisolated from the first layer, and reading a signal from the electricalinterconnect as an indication of the amount of incident light on thesecond layer, where the signal is a charge, voltage, current, or thelike. The pixel circuit may be associated with the reading of the signaland processing signals in response to the signal read. The first layermay be responsive to a first absorption radiation wavelength range andsubstantially transparent to a first transparent radiation wavelengthrange, where the second layer is responsive to at least a portion of thefirst transparent wavelength range.

In embodiments described herein, a quantum dot structure may includeproviding a first quantum dot structure layer, a dielectric on top ofthe first quantum dot structure layer, an isolated electricalinterconnection that at least passes into the first quantum dotstructure layer and the dielectric layer, etching the electricalinterconnection such that an electrically conductive region extendspassed the dielectric layer, and providing a second quantum dotstructure layer on top of the dielectric layer such that it iselectrically associated with the electrically conductive region of theelectrical interconnection.

In embodiments described herein, a multi-layered quantum dot structuremay be calibrated by reading a signal from a first layer of amulti-layered quantum dot structure, determining if the signal isrepresentative of an incident light on the first layer, and applying acorrection factor in relation to the signal to form a corrected signalsuch that the corrected signal represents a calibrated signal. The stepof applying the correction factor further may include calculating thecorrection factor in relation to a signal read from a second layer ofthe multi-layered quantum dot structure.

In embodiments described herein, a quantum dot structure may include afirst layer of first wavelength range responsive quantum dot material, asecond layer of second wavelength range responsive quantum dot material,wherein the second layer is optically stacked on top of the first layer,where the first and second layers form at least a portion of a pixel. Inembodiments, the pixel may be in a Bayer patter; include red, green, andblue layouts; have at least one of red, green, and blue provided in adisproportionate amount. The first wavelength responsive material isresponsive to a prescribed range of wavelengths, where the firstwavelength responsive material may be further responsive to theprescribed range of wavelengths without requiring the use of coloredfilters. The pixel may include a disproportionate amount of second layermaterial to increase the pixel sensitivity to the second wavelengthrange. The first layer may be spin coated onto an integrated circuit.

In embodiments described herein, a photodetector utilizing quantum dotsmay include a multi-layered quantum dot structure comprising at leasttwo quantum dot structure layers, a first exposed layer and a secondexposed layer, separated by a dielectric, wherein the at least twoquantum dot structure layers are adapted to be responsive to differentranges of radiation wavelengths without requiring a colored filter ontop of the first exposed layer.

In embodiments described herein, a camera utilizing quantum dots mayinclude a multilayered photodetector, wherein the multilayeredphotodetector includes at least two optically stacked layers ofphotosensitive materials, a first radiation exposed layer and a secondradiation exposed layer, wherein the first radiation exposed layer ismade of a material that converts a first wavelength range intoelectrical current and transmits a substantial portion of a secondwavelength range, wherein the second radiation exposed layer is made ofa material that converts at least a portion of the second wavelengthrange into electrical current. The first radiation exposed layermaterial may include quantum dot structures. The dielectric layer may bebetween the first radiation exposed layer and the second radiationexposed layer. The electrical interconnection may be electricallyisolated from the second radiation exposed layer and electricallyassociated with the first radiation exposed layer to draw an electricsignal from the first radiation exposed layer in response to firstradiation exposed layer incident light. The at least two opticallystacked layers of photosensitive materials may include at least aportion of a pixel, where the first radiation exposed layer is spincoated onto an integrated circuit.

In embodiments described herein, a quantum dot pixel chip may includeproviding a multilayered quantum dot structure comprising at least twooptically stacked layers of quantum dot materials, a first and secondlayer, wherein the at least two optically stacked layers are made fromdifferent quantum dot materials adapted to respond to differentradiation wavelength ranges; providing a first electrical interconnect,wherein the first electrical interconnect is substantially electricallyisolated from the second layer and is electrically associated with thefirst layer to draw an electric charge from the first layer in responseto first layer incident light within a first layer responsive range;providing a second electrical interconnect, wherein the secondelectrical interconnect is substantially electrically isolated from thefirst layer and is electrically associated with the second layer to drawan electric charge from the second layer in response to second layerincident light within a second layer responsive range; providing adielectric between the first and second layers to provide substantialelectrical isolation of the two layers; providing pixel circuitry toread the electric charge from the first electrical interconnect; andproviding an integrated circuit chip with a processing facility toprocess information relating to the electric charge from the firstinterconnect. The quantum dot pixel chip may be integrated into at leastone of a camera, sensor, viable detector, IR detector, UV detector,x-ray detector, multi-spectral detector, and high gain detector. Memorymay be associated with the pixel circuitry, where the memory provides afunction such as image persistence, frame buffering, or the like. Thefirst layer may be spin coated onto an integrated circuit.

In embodiments described herein, the quantum dot pixel may includeembedded circuitry, associating the embedded circuitry with a function,and connecting quantum dot pixel embedded circuitry to other circuitrywithin the quantum dot pixel chip. The embedded circuitry may include atleast one of a biasing circuit, voltage biasing circuit, current biasingcircuit, charge transfer circuit, amplifier, reset circuit, sample andhold circuit, address logic circuit, decoder logic circuit, memory, TRAMcell, flash memory cell, gain circuit, analog summing circuit,analog-to-digital conversion circuit, and a resistance bridge. Thefunction may include at least one of readout, sampling, correlateddouble sampling, sub-frame sampling, timing, persistence, integration,summing, gain control, automatic gain control, off-set adjustment,calibration, offset adjustment, memory storage, frame buffering, darkcurrent subtraction, and binning. The other circuitry may be located inat least one of a second quantum dot pixel, column circuitry, rowcircuitry, circuitry within the functional components of the quantum dotpixel chip, and circuitry within an integrated system with which thequantum dot pixel chip is associated.

Embodiments of the image sensor described herein include awafer-integrated system. The wafer-integrated system can include variouscombinations of components or elements, for example at least twocomponents, selected from a group that includes: elements embodied insilicon, including but not limited to analog, mixed-signal, and/ordigital circuit elements; QuantumFilm such as described herein; opticalmaterials and elements, including but not limited to lenses, gratings,and/or filters; a component configured to provide autofocusfunctionality to the image sensor, including but not limited to liquidcrystals and/or other optically-tunable materials;Microelectromechanical System (MEMS) elements, including but not limitedto movable actuators, flowing or moving fluids or bubbles, such as thoseto enable the sensing of motion and acceleration.

Embodiments of the image sensor described herein include a bottomelectronic layer that comprises CMOS silicon electronics. The imagesensor also includes one or more additional layers above the CMOSelectronics layer that are configured to include or provide one or moreof the following functions: conversion of the energy contained in lightinto an electronic excitation, such as an electron-hole pair or exciton;retention, or storage, of one or both classes of electronic excitationsfor a known period of time (e.g., 1 nanosecond, 1 microsecond, 1millisecond, 100 milliseconds, a period approximately in the range 1nanosecond to 100 milliseconds; relaying or transferring an electronicsignal, related in a known fashion to the electronic charge contained ina known portion of the material, to an electrical contact connected tothe underlying CMOS silicon electronics, such that the incidence ofphotons over a known period may be estimated based on the electricalsignal collected in the CMOS silicon electronics.

Embodiments of the image sensor described herein include one or morefilms configured to include or provide one or more of conversion of theenergy contained in light into an electronic excitation, such as anelectron-hole pair or exciton, and storage of the generated electronsand/or holes. The stored electrons or holes are transferred out of thefilm at readout time to a circuit node. In embodiments the storage isrealized using potential wells that are formed with impurities insidethe film. The impurities can be injected into the film using diffusion,implantation, self-assembling, and/or a combination of diffusion,implantation, and/or self-assembling. The potential well depth iscontrolled such that the well can be emptied with small amount of biasvoltage, for example approximately 0.1V, approximately 1V, approximately2V, or within a voltage approximately in a range of −5V to 10V. When thewell is empty, the potential of the well is fixed at a level that isdifferent from the potential of the circuit node. The potentialdifference between the film potential well and the circuit node is highenough, for example approximately 0.5V, approximately 0.7V orapproximately in the range of 0.1V to 5V, for the transfer of electronsor holes to be complete before incurring charge sharing effects.

Embodiments of the image sensor described herein include an opticalimaging system comprising non-flat focal plane arrays. The non-flatfocal plane arrays can have one of numerous shaped configurations. As amore specific example of non-flat focal plane arrays, embodiments of theimage sensor described herein include an optical imaging systemcomprising curved focal plane arrays configured to mimic the fieldcurvature. The optical imaging system of an embodiment includes aread-out integrated circuit comprising a crystalline semiconductor suchas silicon. The optical imaging system of an embodiment includes anelectrical interconnect reaching or extending from the surface of thesilicon chip to the top surface of the silicon-based integrated circuit.The optical imaging system of an embodiment includes a curvedconfiguration of the top surface, corresponding to the field curvatureof the image to be projected onto the photodetecting layer lying atopthis surface. The optical imaging system of an embodiment includes aphotodetector layer configured to approximate the curvature of thecurved top surface, and to approximately correspond to the fieldcurvature of the image to be projected onto the top surface. The opticalimaging system of an embodiment can include one or more additionallayers such as layers for passivation, planarization, encapsulation,and/or optical imaging operations to name a few.

Embodiments of the image sensor described herein include stacked pixels.For example, the image sensor includes color pixels comprising a stackof photodetectors, where members of the stack are configured to havediffering sensitivity to different colors of light. For example, thephotodetectors onto which incident light impinges first may absorbprimarily shorter-wavelength light, while the photodetectors onto whichincident light impinges only after passing through one or morephotodetectors may absorb longer-wavelength light. Embodiments includestacked pixels configured to achieve signal-to-noise that is higher, foreach color, relative to a signal-to-noise ratio realized using a Bayerpattern array of 2×2 pixels having the same areal footprint as thestacked pixel.

Embodiments of the image sensor described herein include a stack ofsemiconductor die, interconnected as appropriate to a configuration ofthe image sensor and/or a host device that includes the image sensor.The stacked die of an embodiment are configured to provide a suite offunctions. The suite of functions of an embodiment includes but is notlimited to image sensing, which may include a number of die, where oneor multiple die are configured for some combination of x-ray,ultraviolet, visible, and/or infrared sensing, and where other die areconfigured for some other combination of imaging in these spectralregions. The suite of functions of an embodiment includes but is notlimited to image processing including compression, demosaicing, autowhite balance, autofocus, denoising, deconvolution of signals convolutedby lenses and deconvolution of time-of-flight signals. The suite offunctions of an embodiment includes but is not limited to control ofactuators such as those used in focus and/or zoom to name a few. Thesuite of functions of an embodiment includes but is not limited to thepassive conveyance of heat away from die or the die stack or,alternatively, the active cooling of die or the die stack. The suite offunctions of an embodiment includes but is not limited to thedetermination of spatial position such as implemented using GlobalPositioning System (GPS). The suite of functions of an embodimentincludes but is not limited to the storage of image or other data inmemory. The suite of functions of an embodiment includes but is notlimited to communications, including wired or wireless communications,with other elements in the system, wherein the communications includethe use of protocols such as Bluetooth, Machine Independent ParallelInterface (MIPI) protocol, etc.

Embodiments described herein include a color image sensor that does notrequire a separate, lossy color filter layer. Instead, these embodimentscomprise a focal plane array that includes a patterned array ofphotosensitive materials, where different materials within this arraypossess different sensitivities to different colors of the x-ray, UV,visible, and infrared optical spectrum. A demosaicing algorithm is thenemployed to estimate the intensities associated with each spectralcomponent.

Embodiments of the image sensor described herein include a circuitconfigured to incorporate, include, or integrate at least onecombination of the following components or elements: a photosensitivelayer configured to include quantum film; circuitry configured forcollecting, storing, amplifying, and interconverting electronic signalsfrom the photosensitive layer; circuitry configured for storing digitalinformation.

Embodiments of the image sensor described herein are configured toprovide autofocus functionality. The image sensor includes an array ofcircuitry, and a photosensitive layer, configured for image sensing,circuitry configured for the estimation of whether the resultant imageis in focus, and circuitry configured for the conveyance of signals toan actuator, or actuators, that alter the focus of the system of lensesonto the image sensor.

Embodiments of the image sensor described herein are configured toprovide antishake functionality. The embodiments configured forantishake include at least one combination of the following: an array ofcircuitry, and a photosensitive layer, configured for image sensing; amechanism, such as an accelerometer, configured to provide signals fromwhich it is possible to estimate the motion of the module; circuitryconfigured to estimate whether the module is in motion, and that mayinclude estimation of the direction, velocity, and acceleration of themodule; circuitry or software configured to combine, with the aid ofcertain spatial transformation operations, a series of images obtainedunder motion of the sensor, in such a way as to cancel, in some part,the influence of motion during the acquisition of frames.

Embodiments described herein include a deconvolution algorithm based onconcurrent image data from multiple imaging planes, such that animproved image or picture is generated using image data captured atdifferent depths of focus. In conventional optical imaging systems, theoptical field projected onto a focal plane array is generally nonplanar.This necessitates the use of imaging optics that retain a depth of focussufficient to capture an acceptable image using a single, planary focalplane array. In embodiments, a multiplicity of planar image sensors isstacked atop one another. The data of each image sensor can beindependently read, including sequential read operations and/or parallelread operations. The curvature of the optical plane is known, and asingle two-dimensional (X-Y) image is reconstituted by estimating theoptical field intensity at the most-in-focus vertical position(Z-dimension) pixel at that X-Y coordinate. As a result, low-F-number(e.g., 2 and below) optics are employed, resulting in high opticalcollection efficiency, low-light-sensitivity, and enhancedsignal-to-noise ration, while preserving an in-focus image.

Embodiments of the image sensor described herein include microlenses.The image sensors with microlenses of an embodiment include an array ofcircuitry. The image sensors with microlenses of an embodiment include aphotosensitive layer. The image sensors with microlenses of anembodiment include one or more layers configured for passivation of thephotosensitive layer. The image sensors with microlenses of anembodiment include one or more layers configured for altering thereflection of the system. The image sensors with microlenses of anembodiment include one or more layers configured for filtering certainportions of the optical spectrum. The image sensors with microlenses ofan embodiment include an array of curved optical elements configured toconcentrate optical power incident on each pixel into a primary regionfor sensing within the portion of the photosensitive layer associatedwith each pixel element.

Embodiments of the image sensor described herein provide reduced opticalcrosstalk. The embodiments offering reduced optical crosstalk include atop-surface photodetector configured so that light of a range of visibleand other colors is substantially absorbed within a thin layer. The thinlayer of an embodiment includes a layer with a thickness approximatelyin a range of from 200 to 500 nm. The thin layer of an embodimentincludes a layer with a thickness approximately in a range of from 200to 1 um. The thin layer or an embodiment includes a layer with athickness approximately in a range of from 200 to 2 um. The embodimentsminimize lateral crosstalk between adjacent pixel elements through thenear-complete absorption of light within the relatively thin layer.

Embodiments of the image sensor described herein provide simplifiedcolor processing relative to conventional image sensors. The embodimentsproviding simplified color processing include circuitry, software, or acombination thereof, configured for the estimation of the intensityassociated with certain colors incident on certain pixels. The reductionof optical crosstalk realized through use of the estimation of anembodiment allows for a color or intensity-estimation algorithm inembodiments that requires only the signal associated with a particularpixel, and does not require signal information for nearby pixels. Theestimation also may provide higher photo response with a higher degreeof uniformity.

Embodiments of the image sensor described herein provide watermarkrecognition. Embodiments include an imaging system, and an object to beimaged, wherein the object to be imaged is configured to include adistinctive spatial, chromatic, or spatial-chromatic pattern which marksthe object as authentic, or which provides data for look-up in adatabase for authentication or asset classification or assetrecognition. The imaging system of these embodiments is configured topossess the sensitivity, in all wavelengths of light (includingultraviolet, visible, and infrared), to enable the recognition of thedistinctive spatial, chromatic, or spatial-chromatic pattern. Theimaging system of an embodiment includes an illumination deviceconfigured to illuminate the object, including illuminating in atime-resolved and/or spectrally-resolved fashion.

The imaging system with the image sensor of an embodiment can also beconfigured to inject artificial marks into captured or processed images.Embodiments include an optical imaging system that includes an imagesensor, collection and focusing optics, and an optical source. Theoptical source emits light of a wavelength that may or may not bevisible to the human eye, but which may be detected using some portionof, or all, pixels that comprise the image sensor. The object, whichpossesses distinguishing chromatic features in the wavelength of theoptical source, is illuminated using the optical source. In this mannerthe object is labeled for covert recognition and/or authentication.

Embodiments of the image sensor described herein provide stereoscopicimaging. Embodiments include an imaging system onto which a multiplicityof images may be projected, including using different wavelengths and/orat different points in time, from multiple perspectives. Theseembodiments include circuitry and software for the transformation ofthis multiplicity of images into a stereoscopic project, or into a formof image data that includes information on depth as well as lateralilluminance.

Embodiments of the image sensor described herein provide motionrecognition of image elements (e.g., a baseball bat in gaming, etc.).Embodiments include an imaging system, and an object to be included attimes in imaging. The object includes but is not limited to distinctivespatial-chromatic markings, such that the lateral, and/or depth, and/orrotational motion, of the objected may be accurately determined by theimage sensor and associated components based on a series of images. Theimage system is configured to include the capacity to measure thespatio-temporal-chromatic patterns produced by the object.

In embodiments, integrated circuitry may be included in the quantum dotpixel chip, including a plurality of layers of integrated circuitry thatunderlie the quantum dot pixel array, and associated with imageprocessing. The layers of integrated circuitry may be connected with thequantum dot pixel array, where the connection is such that theintegrated circuitry and the quantum dot pixel array may form a singlesemiconductor chip. In embodiments, the quantum dot pixel array may bemounted onto the integrated circuitry to form a hybrid integratedcircuit structure. The integrated circuitry may have a function, wherethe function includes at least one of high-speed readout, signalmultiplexing, decoding, addressing, amplification, analog-to-digitalconversion, binning, memory, image processing, and image sensorprocessing. The layers may include electrical interconnects, where theinterconnects are between electrical components, where the electricalcomponents may be within at least one of quantum dot pixel chipintegrated circuitry, quantum dot pixel circuitry, integrated systemcircuitry, input to the quantum dot pixel chip, and output from thequantum dot pixel chip. The integrated circuitry may include improvedcharacteristics, where the characteristics include at least one ofhigh-speed readout, low-noise readout, small die area, larger processgeometries, combined analog and digital circuitry, higher levels ofintegration, image processing capabilities, low power, single voltagedesigns, and increased detector fill factor.

In embodiments, the quantum dot pixel chip may be integrated into adevice, where the device is selected from the group consisting of acamera, a cell phone handset, a digital still camera, a video camcorder,a security camera, a web camera, a night vision device, night visiongoggles, a night vision scope, a no-shake camera, a low-light camera, ablack and white in low light and color in high light camera and amulti-spectral camera. The device may include an image sensor with atleast one a top-surface quantum dot photodetector, a high fill-factorarrangement of quantum dot pixels, a wide chief ray angle configurationof quantum dot pixels, and a high-sensitivity photodetector. The quantumdot pixel chip may provide automated gain control within the quantum dotphotodetector. The device may include a tunable materials system fortop-surface photodetection that responds to different energies ofphotons, where the different energies are selected from the groupconsisting of x-ray, ultraviolet, infrared, and visible energies. Thedevice may be for at least of aircraft wing inspection, a machine visionapplication, integration of a camera on a robotic arm, multi-spectralinspection of products, simultaneous image and edge detection duringinspection and counting, low-light inspection, integrated imageprocessing for control algorithms, high resolution high gain cameras,pattern recognition, pattern detection, stored calibration of images inmemory, medical image sensing, detection of laser targeting whilesimultaneously providing an image of an environment, all-conditionviewing when used by an individual, and vehicle-based image-sensing.

In embodiments, regions of a photoconductive layer are electricallycontacted by an array of electrodes. It is important to achieveconsistent, robust mechanical and electrical contact between thephotoconductive layer and the electrical contacts. Following fabricationof the electrical contacts, there may exist residual oxides,oxynitrides, or organic materials. In embodiments, it may be importantto remove the organic materials; this may be accomplished using anoxygen plasma etch, an acid-alkaline clean, an alkaline-acid clean, orcombinations thereof. In embodiments, it may be important to remove theoxides and/or the oxynitrides; this may be accomplished using a dry etchor a wet etch. thin barrier layer atop the electrical contacts, prior tothe deposition of the photoconductive layer.

In embodiments, it may be important to achieve electrical contactthrough a thin barrier layer between the electrical contacts mentionedabove and the photoconductive layer. In this instance, it is importantto remove oxides, oxynitrides, and/or organic materials of unknown oruncontrolled thickness; and then to deposit, or otherwise form, acontrolled thin barrier layer atop the electrical contacts, prior to thedeposition of the photoconductive layer.

In embodiments, in order to achieve robust mechanical and electricalcontact of the photoconductive layer to the electrical contacts, anadhesion material may be employed. This material may contain a moietyhaving an affinity to the materials at the surface of the electricalcontacts, and another moiety having an affinity to the materials at thesurface of the constituents of the photoconductive layer. As oneexample, if the electrical contacts are terminated with TiN (titaniumnitride) or an oxynitride thereof, then one moiety in the adhesion layermay be an amine functional group. As another example, if thephotoconductive layer includes a metal such as Pb, Cd, Cu, In, or Bi,then one moiety in the adhesion layer may be a thiol functional group.Such an adhesion, or anchor, layer may be applied by spin-casting,dip-coating prior to, during, or following deposition of some or all ofthe photoconductive layer.

In embodiments, electrical contacts having a deep work function, such asa work function lower than 4.4 eV or 4.6 eV or 4.8 eV below the vacuumlevel, may be employed. If a binary alloy such as TiN (titanium nitride)is employed, the work function may be deepened by controlling the ratioof Ti to N during formation of the alloy. For example, a high ratio(greater than 1:1) of N to Ti may be used.

In embodiments, electrical contacts having a specific work function maybe desired. The work function of an already-patterned set of electricalcontacts may be modified by first depositing a thin layer of anothermaterial, such as, for example, a 10 nm layer of Au, Pd, Pt, or Ni; andthe continuity of this deposited layer may then be deliberatelydisrupted using a selective lift-off technique wherein deposited metalscovering a region where the metals are not desired are lifted offthrough selective etching of the non-contacting material (e.g. bufferedoxide etching of an oxide in the non-contacting regions)

In embodiments, electrical contacts having a specific work function maybe desired. The work function of an already-patterned set of electricalcontacts may be modified by (1) treating the sample, throughspin-coating, dip-coating, spray-coating, or other method, with amaterial that adheres selectively to materials over which electricalcontact is not desired; (2) depositing a thin layer of another material,such as, for example, a 10 nm layer of Au, Pd, Pt, or Ni; and (3) thencleaning the wafer to lift off the deposited layer in regions wherecontact is not desired.

In embodiments, pixel binning may be employed, wherein the signalcorresponding to a multiplicity of smallest-patterned-pixels may beaccumulated within a single superpixel. The accumulation can be achievedin digital domain, in analog domain, or at film level. Take the exampleof accumulating the signal corresponding to a 2×2 array into a singlesuperpixel: It can be achieved using film binning by applying a biasacross the entire set of 2×2 pixels and integrating into a singlecapacitor. It can also be achieved using analog binning by sum up thecharge stored in the 4 individual capacitors, or using digital binningafter the signal is digitized.

In embodiments, the photocurrent passing through the photoconductivelayer, and collected in a given pixel, may have a nonlinear relationshipwith the intensity impinging on that pixel. In embodiments, thisnonlinear relationship may be sublinear, thus the photoconductive gainmay diminish with increasing intensity. In embodiments, it may bedesired to provide an estimate of the intensity impinging on the pixelduring the integration period based on the collected current. Inembodiments, it may be desirable to estimate the functional relationshipbetween intensity and photocurrent, Photocurrent=f(Intensity), and todetermine, or estimate, the inverse of this function,Intensity=f⁻¹(Photocurrent). In embodiments, the functional relationshipbetween intensity and photocurrent may be characterized duringproduction or assembly and a representation be stored on or off devicefor use by a post processing digital algorithm that will invert (f⁻¹)the intensity-photocurrent mapping function(f). In embodiments, a signalproportional to the inferred intensity may be generated, by theimplementation of an analog function that approximately inverts (f⁻¹)the intensity-photocurrent mapping function (f).

In embodiments, the voltage spacing among the levels of ananalog-to-digital converter may be manipulated, including being madenonuniform, such as to compensate for the nonlinear photocurrent vs.intensity relationship mentioned above.

In embodiments, further arithmetic operations may be implemented in thedigital domain to produce a revised digital estimate of the impingingintensity based on the observed digital estimate of the photocurrent oraccumulated photocharge.

In embodiments, an integrated fingerprint sensor may be implemented bycombining (1) An array of photoconductive regions independent read usinga read-out integrated circuit (2) A source of illumination in thevisible, or in the infrared, or both, that illuminates the subject to beread, and provides a signal for the photoconductive regions of (1) tosense.

In embodiments, pixel can change shapes from one layer to another layer,while maintaining the same pixel area. From example, in quantum filmlayer the pixel can have square shape while in silicon layer the pixelhas rectangular shape. As another example, if the film layer pixel is 2um×2 um, the silicon layer pixel can be 4 um×1 um: so putting together 4silicon layer pixels in a row gives a total area of 4 um×4 um, whichcorresponds to 2×2 array of film layer pixels. Utilizing this pixelshape flexibility one can achieve very high pixel sharing such as16-to-2 sharing, which means 16 pixels can be read out using 2 sets ofreadout transistors.

In embodiments, the film can be used in direct integration mode.Normally the film is treated as a photo-resistor that changes current orresistance with light level. In this direct integration mode, the filmis biased to be a direct voltage output device. The voltage level directindicates the incident light level.

In embodiments, the quantum film signal can be read out usingtransistors that have high noise factors. For example, thin oxidetransistors can be used to read out quantum film signal, with thepresence of large leakage current and other noise sources of thetransistors themselves. This becomes possible because the film hasintrinsic gain which helps suppress the transistor noise.

Further example embodiments follow, including example embodiments of orincluding one or more of the materials, systems, devices and methods,described above and/or within the scope of the teachings presentedherein.

Embodiments include an optically sensitive layer having aphotoconductive gain determined by a prior temperature excursion,wherein greater application of elevated temperatures decreases the gain;wherein the temperature excursion is determined by the photoconductivegain, wherein the elevation of the gain increases current flow andresults in elevated temperature; and wherein, upon continuousfixed-intensity illumination for a time period, the photoconductive gainreaches a substantially same final value independent of an initial valueof the gain.

Embodiments include a photovoltaic device for converting optical powerinto electrical power, comprising: a first electrode having a deep workfunction deeper than approximately −4.6 eV; a nanocrystalline layercomprising colloidal quantum dot cores connected using linker moleculesthat span the surfaces of the cores; and a shallow work functionelectrode having a work function shallower than approximately −4.4 eV.

Embodiments include a photovoltaic device for converting optical powerinto electrical power, comprising: a first junction device having abandgap less than approximately 1.2 eV; a second junction device havinga bandgap greater than approximately 1.5 eV; wherein the devicescomprise the same chemical constituents, the chemical constituentsarrayed to form nanoparticles having a diameter greater thanapproximately 4 nm in the first layer, and to form nanoparticles havinga diameter less than approximately 3 nm in the second layer.

Embodiments include a method of making an optically sensitive layer,comprising: placing a nanoparticle-containing colloidal dispersion inproximity to a substrate; inducing graduate precipitation of thenanoparticle-containing dispersion onto the substrate through theaddition of a precipitating or crosslinking moiety.

Embodiments include an optically sensitive layer having a conductanceexceeding 3E-12 ohm*cm under approximately 1 lux green illumination, andthe optically sensitive layer having a conductance of less than 1E-13ohm*cm in the dark; and wherein, following turn-off of the illumination,conductance of the optically sensitive layer substantially returns toits dark conductance within less than 100 milliseconds.

Embodiments include an image sensor comprising: at least one opticallysensitive layer; a periodic array of spectrally-selective filters;wherein an image possessing spectral information is constructed throughknowledge of the absorption spectra, and spatial locations of, thespectrally-selective filters; wherein the spectral information includesat least one of red, green, blue, ultraviolet, and infrared spectralinformation.

Embodiments include an image sensor comprising: a first region ofoptically sensitive material; a second region of optically sensitivematerial; and wherein the first and second region possess substantiallydifferent spectral onset of absorption; and wherein an image possessingspectral information is constructed through knowledge of the absorptionspectra, and spatial locations of, the first and second regions; whereinthe spectral information includes at least one of red, green, blue,ultraviolet, and infrared spectral information.

Embodiments include an image sensor system-on-chip that includes: anoptically sensitive layer; digital circuitry providing for a substantialreduction in the number of digital bits describing the resultant imagerelative to the raw digital pattern generated by the sensor.

Embodiments include an image sensor that includes: a first opticallysensitive layer; a second optically sensitive layer; wherein the imagesensor generates two overlaid images, the first image comprising arepresentation of the visible-spectral-domain content incident on theimage sensor, and the second image comprising a representation of aninterval-spectral-domain content incident on the image sensor, whereinthe interval includes at least one of red, green, blue, ultraviolet, andinfrared spectral information.

Embodiments include an image sensor including: at least one opticallysensitive layer; an array of electrodes in contact with the opticallysensitive layer which are arrayed in a hexagonal (honeycomb) pattern.

Embodiments include an image sensor including: at least one opticallysensitive layer; an array of electrodes in contact with the opticallysensitive layer which are arrayed in a triangular (honeycomb) pattern.

Embodiments include an image sensor including: at least one opticallysensitive layer; at least one element that disperses incident radiationinto spectral components whose angles of incidence on the opticallysensitive layer are determined by their wavelengths.

Embodiments include an image sensor including: at least one opticallysensitive layer; at least one element that disperses incident radiationinto spectral components whose spatial positions of incidence onto theoptically sensitive layer are determined by their wavelengths.

Embodiments include an image sensor including at least one opticallysensitive layer, wherein light is substantially absorbed for angles ofincidence ranging from approximately 0 to 35 degrees measured relativeto a perpendicular to the optically sensitive layer.

Embodiments include a pixilated array including at least one opticallysensitive layer, wherein the pixilated regions are optically isolatedfrom one another using a substantially optically absorbing or reflectingintervening material.

Embodiments include an image sensor including at least one opticallysensitive layer wherein: a first region of the optically sensitive layerprovides electronic signals related to the intensity incident on thatregion and lying within a first spectral region; a second region of theoptically sensitive layer provides electronic signals related to theintensity incident on that region and lying within a second spectralregion; wherein digital representations of the results visible and x-rayimages are conveyed from the sensor. The first spectral region of anembodiment is one or more of a visible spectral region, an X-rayspectral region, an ultraviolet (UV) spectral region, a near infrared(IR) (NIR) spectral region, a short-wavelength IR (SWIR) spectralregion, and a mid-wavelength IR (MWIR) spectral region in anycombination with the second spectral region of an embodiment, which isone or more of a visible spectral region, an X-ray spectral region, anultraviolet (UV) spectral region, a near infrared (IR) (NIR) spectralregion, a short-wavelength IR (SWIR) spectral region, and amid-wavelength IR (MWIR) spectral region.

Embodiments include an imaging system including: at least one opticallysensitive layer; at least one optical source; wherein a distance ofobjects in the imaging system's field of view may be ascertained towithin 10 feet.

Embodiments include an imaging system including: at least one opticallysensitive layer; at least one optically sensitive device capable ofdistinguishing optical signals space more than ten nanoseconds apart;wherein a distance of objects in the imaging system's field of view maybe ascertained to within 10 feet.

Embodiments include an imaging system including at least one opticallysensitive layer; wherein a three-dimensional spatial representation ofobjects lying within the system's field of view is conveyed from theimaging system.

Embodiments include an array of photodetecting elements integrated on anelectronic circuit including at least one optically sensitive layer;wherein at least approximately 70% of photons incident on the array areabsorbed within the optically sensitive layer.

Embodiments include an array of photodetecting elements integrated on anelectronic circuit including at least one optically sensitive layer;wherein, for at least one wavelength of light, the power absorbed fromlight propagating back towards the source of illumination is greaterthan approximately 20% of the power absorbed from light propagating fromthe source of illumination forwards towards the array.

Embodiments include a device comprising at least one first opticallysensitive region combined with at least one other optically sensitiveregion that is partially obscured by the first optically sensitiveregion; wherein an electronic signal related to the difference inconductance of the two regions is reported using an electronic circuit.

Embodiments include a device comprising at least one optically sensitiveregion combined with at least one other optically sensitive region thatis partially or substantially obscured from illumination; wherein anelectronic signal related to the difference in conductance of the tworegions is reported using an electronic circuit.

Embodiments include an image sensor comprising an optically sensitivelayer overlaid on an electronic circuit fabricated using a standardcomplementary metal oxide semiconductor (CMOS) process.

Embodiments include an image sensor comprising a first opticallysensitive region adjacent to, but separated from, a second opticallysensitive region.

Embodiments include an method of making a first optically sensitiveregion adjacent to, but separated from, a second optically sensitiveregion; wherein a single continuous optically sensitive region is firstformed, and the region is then cloven into separate regions through achange in the volume of the optically sensitive region.

Embodiments include a photodetector comprising: an optically sensitiveregion; a first electrode pair across which a voltage bias approximatelyin a range of 0.1 to 10 v is applied; a second electrode pair; wherein acircuit is configured to measure the potential difference between theelectrodes in the second electrode pair.

Embodiments include an image sensor comprising at least: one opticallysensitive region; a substantially transparent material covering theoptically sensitive region.

Embodiments include an image sensor comprising at least: one opticallysensitive region; a substantially transparent material covering theoptically sensitive layer and having a refractive index different by atleast 0.5 compared to the refractive index of the optically sensitivelayer.

Embodiments include an image sensor comprising: an optically sensitivelayer; and an adhesion layer anchoring the constituents of the opticallysensitive layer to an electronic circuit.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodecomprises titanium nitride; and wherein the optically sensitive layer isin electrical communication with the electrode.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodeincludes a region comprising titanium oxynitride; and wherein theoptically sensitive layer is in electrical communication with theelectrode.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodecomprises platinum; and wherein the optically sensitive layer is inelectrical communication with the electrode.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodecomprises nickel; and wherein the optically sensitive layer is inelectrical communication with the electrode.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodecomprises copper; and wherein the optically sensitive layer is inelectrical communication with the electrode.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodecomprises tantalum nitride; and wherein the optically sensitive layer isin electrical communication with the electrode.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodecomprises tantalum oxynitride; and wherein the optically sensitive layeris in electrical communication with the electrode.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodecomprises aluminum; and wherein the optically sensitive layer is inelectrical communication with the electrode.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodecomprises aluminum oxide; and wherein the optically sensitive layer isin electrical communication with the electrode.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodecomprises gold; and wherein the optically sensitive layer is inelectrical communication with the electrode.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodecomprises palladium; and wherein the optically sensitive layer is inelectrical communication with the electrode.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodecomprises platinum Sulfide (PtS); and wherein the optically sensitivelayer is in electrical communication with the electrode.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodecomprises palladium sulfide (PdS); and wherein the optically sensitivelayer is in electrical communication with the electrode.

Embodiments include an image sensor comprising at least one opticallysensitive layer and at least one electrode; wherein the electrodecomprises Gold sulfide (AuS); and wherein the optically sensitive layeris in electrical communication with the electrode.

Embodiments include an image sensor comprising: at least one opticallysensitive layer; a circuit, at least one node of which is in electricalcommunication with the optically sensitive layer; wherein the circuitprovides for amplification of the electrical current traversing theoptically sensitive layer.

Embodiments include an image sensor comprising: at least one opticallysensitive layer; a circuit, at least one node of which is in electricalcommunication with the optically sensitive layer, wherein the circuitresets a charge store to a predetermined voltage.

Embodiments include an image sensor comprising: at least one opticallysensitive layer; a circuit, at least one node of which is in electricalcommunication with the optically sensitive layer; wherein the circuitstores an electrical signal proportional to the integrated intensityfalling on the optically sensitive layer over the course of a prescribedintegration period.

Embodiments include an image sensor comprising: at least one opticallysensitive layer; a circuit, at least one node of which is in electricalcommunication with the optically sensitive layer; wherein the circuitgenerates a digital representation related to the integrated intensityfalling on the optically sensitive layer over the course of a prescribedintegration period

Embodiments include an image sensor comprising: at least one opticallysensitive layer; a circuit which provides an electrical signal relatedto the difference between the voltage at a node immediately prior to theintegration of current from the optically sensitive layer and thevoltage at the same node immediately following the integration ofcurrent from the optically sensitive layer.

Embodiments include an image sensor comprising: at least one opticallysensitive layer; and a circuit that sets the integration period tomaximize the usable dynamic range of the image.

An image sensor comprising: at least one optically sensitive layer; anda circuit that sets the electronic gain to maximize the usable dynamicrange of the image.

Embodiments include an image sensor comprising: at least one opticallysensitive layer; and a circuit that subtracts from each pixel a valuerelated to the dark current generated in that pixel.

Embodiments include an image sensor comprising: at least one opticallysensitive layer; and a circuit that subtracts from each image a storedreplica of a dark image.

Embodiments include an image sensor comprising: at least one opticallysensitive layer; and a circuit that first subtracts from each image astored replica of a dark image, and then divides the result by a storedreplica of a light frame from which the same dark image has previouslybeen subtracted.

Embodiments include an image sensor comprising: at least one opticallysensitive layer; and a circuit that enables the storage of digital data.

Embodiments include an image sensor comprising: at least one opticallysensitive layer; and a circuit that stores a dark frame.

Embodiments include an image sensor comprising: at least one opticallysensitive layer; and a circuit that stores a light frame taken underknown illumination.

Embodiments include an image sensor comprising: at least one opticallysensitive layer; and a circuit that stores the difference between alight frame taken under known illumination and a dark frame.

Embodiments include an image sensor comprising: an optically sensitivelayer; and a read-out circuit which reports an average over multiplesamples of a voltage related to the intensity of illumination on theoptically sensitive layer.

Embodiments include an optical system comprising: an optically sensitivelayer; and a source of illumination in a wavelength band to which theoptically sensitive layer is responsive.

Embodiments include an image sensor comprising: an optically sensitivelayer; and a circuit that provides an output image related to thederivative in time of the illumination of the sensor.

Embodiments include an optically sensitive layer comprisingclosely-packed semiconductor nanoparticle cores, wherein each core ispartially covered with an incomplete shell, where the shell producestrap states having substantially a single time constant.

Embodiments include an optically sensitive layer comprising nanocrystalcores passivated using ligands of at least two substantially differentlengths.

Embodiments include an optically sensitive layer comprising nanocrystalcores passivated using at least one ligand of at least one length, andpassivated and crosslinked using at least one crosslinking molecule ofat least one length.

Embodiments include a semiconductor nanoparticles comprising PbS whichare partially or completely covered with a shell of PbSO3.

Embodiments include a partially oxidized PbS core which is substantiallylacking in PbSO4 (lead sulfate).

Embodiments include an a color-sensitive pixel comprising: aphotoconductive material; and a wavelength-selective-light-absorbingmaterial.

Embodiments include are directed to a method of making a color-sensitivepixel, wherein a photoconductive material and a wavelength-selectivelight-absorbing material substantially phase-segregate in the course ofprocessing, resulting in a top portion of a pixel being constitutedprincipally of the wavelength-selective-optically-absorbing material,and the bottom portion of the pixel being constituted principally of thephotoconductive material.

Embodiments include a device comprising an optically sensitive layer anda circuit made using thin-oxide transistors.

Embodiments include an optically sensitive layer having responsivitygreater than 1 A/W throughout the entire spectral region 400 nm to 1600nm.

Embodiments include an imaging system including providing for passivenight vision based on illumination due to the atmospheric nightglow.

Embodiments include an image sensor system-on-chip comprising: anoptically sensitive layer; and a means of storing a plurality of frames.

Embodiments include an image sensor system-on-chip comprising: anoptically sensitive layer; and a means of storing a plurality of frames;wherein the image sensor provides high-rate video compression.

Embodiments include an image sensor system-on-chip comprising: anoptically sensitive layer; and a means of storing a plurality of frames;wherein the image sensor ascertains inter-frame motion and implementsimage stabilization by combining suitably x-y-shifted frames.

Embodiments include an image sensor system-on-chip comprising: anoptically sensitive layer; and a means of ascertaining and storing thelocations of nonresponsive pixels.

Embodiments include an image sensor system-on-chip comprising: anoptically sensitive layer; a means of ascertaining and storing thelocations of pixels having a leakage current higher than a predeterminedthreshold.

Embodiments include an image sensor system-on-chip comprising: anoptically sensitive layer; a circuit and algorithm to generate a spatialFourier transform of the image.

Embodiments include an image sensor system-on-chip comprising: anoptically sensitive layer; a circuit and algorithm to optimize theexposure conditions.

Embodiments include an imaging system comprising: an image sensorincluding an optically sensitive layer; a circuit and algorithm toimplement autofocus.

Embodiments include an image sensor comprising: a substrate; ananocrystalline film over a portion of the substrate; a substantiallycontinuous layer conformally covering the nanocrystalline film and theexposed portions of the substrate, wherein gases, liquids, and solids donot permeate the nanocrystalline film.

Embodiments are directed to an imaging system comprising: an imagesensor circuit comprising an optically sensitive layer; at least oneelement, monolithically integrated with the image sensor circuit, andselected from a group consisting of: analog, mixed-signal, and/ordigital circuit elements; optical materials and elements, including butnot limited to lenses, gratings, and/or filters; a component configuredto provide autofocus functionality to the image sensor, including butnot limited to liquid crystals and/or other optically-tunable materials;Microelectromechanical System (MEMS) elements, including but not limitedto movable actuators, flowing or moving fluids or bubbles, such as thoseto enable the sensing of motion and acceleration.

Embodiments include an image sensor comprising an optically sensitivelayer which is nonplanar and which is conformably formed on theunderlying substrate.

Embodiments include an optical system comprising: an image sensorcomprising an optically sensitive layer; and at least one additionalsemiconductor die.

Embodiments include an imaging system comprising: an optically sensitivelayer; circuitry configured for the estimation of whether the resultantimage is in focus; and circuitry configured for the conveyance ofsignals to at least one actuator that alters the focus of the system oflenses onto the image sensor.

Embodiments include an imaging system comprising: an optically sensitivelayer; a means of estimating the motion of the imaging system; circuitryconfigured to estimate imaging system motion including at least one of:the direction, velocity, and acceleration of the module; circuitry orsoftware configured to combine, with the aid of certain spatialtransformation operations, a series of images obtained under motion ofthe sensor, in such a way as to cancel, in some part, the influence ofmotion during the acquisition of frames.

Embodiments include an image sensor comprising: a first opticallysensitive layer; a second optically sensitive layer; wherein the firstand second optically sensitive layer are responsive to a similarspectral region; and where the second optically sensitive layer allowstransmission of greater than approximately 50% of light incident on itdown to the first optically sensitive layer.

Embodiments include an imaging system comprising: an image sensorcomprising an optically sensitive layer; a plurality of lenses providingan f-number less than approximately 2.8.

Embodiments include an image sensor comprising: a first opticallysensitive layer; at least one substantially transparent interlayer; andan array of curved optical elements that determine the distribution ofintensity across the optically sensitive layer.

Embodiments include an imaging system, and an object to be imaged,wherein the object to be imaged is configured to include a distinctivespatial, chromatic, or spatial-chromatic pattern which marks the objectas authentic, or which provides data for look-up in a database forauthentication or asset classification or asset recognition.

Embodiments include an imaging system, wherein an object to be imagedincludes a distinctive spatial, chromatic, or spatial-chromatic patternwhich marks the object as authentic, or which provides data for look-upin a database for authentication or asset classification or assetrecognition.

An imaging system onto which a multiplicity of images may be projected,including using different wavelengths and/or at different points intime, from multiple perspectives. These embodiments include circuitryand software for the transformation of this multiplicity of images intoa stereoscopic project, or into a form of image data that includesinformation on depth as well as lateral illuminance.

Embodiments include an integrated fingerprint sensor comprising: anarray of photoconductive regions independently read using a read-outintegrated circuit; a source of illumination in one or more of a visibleand infrared spectrum that illuminates the subject to be read, andprovides a signal for sensing by the photoconductive regions.

Embodiments are directed to a photoconductive photodetector havingresponsivity greater than approximately 0.4 A/W and a substantiallysingle-valued persistence time of less than approximately 100 ms.

Embodiments include a photoconductive photodetector having responsivitygreater than approximately 0.4 A/W, and having photocurrent, followingthe turn-off of illumination, that returns substantially to its darkcurrent value within less than approximately 200 ms.

Embodiments include a nanocrystalline solid substantially possessing asingle trap state lifetime, or persistence time, in the range ofapproximately 1 ms to 100 ms.

Embodiments include a nanocrystalline solid in which a portion of thenanocrystal’ surfaces are oxidized, wherein a first set of native oxidesare excluded and a second set of native oxides are present. The firstset of native oxides includes PbSO4, for example. The second set ofnative oxides includes PbSO3, for example.

Embodiments include a nanocrystalline solid in which trap states providepersistence, wherein the energy to escape from the predominant trapstates is less than or equal to approximately 0.1 eV, wherein thereexists a much lower concentration of trap states having energy greaterthan or equal to approximately 0.2 eV.

Embodiments include a photoconductive photodetector in whichsubstantially a single chemical species has associated with it asubstantially single energy depth and thus, at a given temperature, asubstantially single trap state lifetime, and thus a substantiallysingle temporal component associated with the rise and fall ofphotocurrent during incident optical transients.

Embodiments include a photoconductive photodetector in whichsubstantially a single chemical species has associated with it asubstantially single energy depth and thus, at a given temperature, asubstantially single trap state lifetime, and thus a substantiallysingle temporal component associated with the rise and fall ofphotocurrent during incident optical transients. The single chemicalspecies of an embodiment is PbSO3 (lead sulfite). The single energydepth of an embodiment is approximately 0.1 eV. The substantially singletrap state lifetime of an embodiment, at room temperature, isapproximately 30 milliseconds. The substantially single temporalcomponent associated with the rise and fall of photocurrent in anembodiment is approximately 30 milliseconds.

Embodiments include a photoconductive photodetector in whichsubstantially a single chemical species has associated with it asubstantially single energy depth and thus, at a given temperature, asubstantially single trap state lifetime, and thus a substantiallysingle temporal component associated with the rise and fall ofphotocurrent during incident optical transients. The photoconductivemedium of the photodetector of an embodiment is substantially devoid oflead sulfate PbSO4, having depth 0.3 eV or greater, and having transientcomponent of order seconds. The photoconductive medium of thephotodetector of an embodiment is substantially devoid of leadcarboxylate, having depth 0.2 eV or greater, and having transientcomponent of order half a second or more. Other chemical species may bepresent in the photoconductive medium if they do not have associatedwith them trap states. For example PbS may be used as the basis for thephotoconductive semiconductor medium; and organic ligands such asethanethiol, ethanedithiol, butanethiol, butanedithiol, hexanethiol,hexanedithiol, dodecanethiol, and dodecanedithiol, and their complexeswith Pb, may all be included.

Embodiments include an optically sensitive layer comprisingsubstantially fused nanocrystal cores having a dark current density lessthan approximately 0.1 nA/cm2.

Embodiments include an optically sensitive layer comprisingsubstantially fused nanocrystal cores, wherein the nanocrystals arepassivated using a chemical functional group, wherein the passivatingmoiety includes a conductive crosslinker.

The nanocrystals of an embodiment are passivated using a chemicalfunctional group including one or more of thiol, amine, and carboxylate.The passivating moiety of an embodiment is a conductive crosslinkerincluding one or more of benzene, dibenzene, and tribenzene.

Embodiments include an optically sensitive layer including ofsubstantially fused nanocrystal cores, wherein the nanoparticlessurfaces are passivated to provide persistence less than approximately100 microseconds duration.

Embodiments include an optically sensitive layer that overlies twoelectrodes, wherein one electrode includes a material having workfunction deeper than approximately −4.6 eV, and the other electrodeincludes a material having work function shallower than approximately−4.4 eV.

Embodiments include an image sensor in which the predominant directionof photocurrent flow within each pixel is parallel to the surface of theintegrated circuit.

Embodiments include a colloidal quantum dot solid in which thepredominance of minority carriers are able to diffuse over a distance ofmore than approximately 100 nm prior to recombining.

Embodiments include a colloidal quantum dot solid in which, under theapplication of an electric field exceeding approximately 10E4 V/um, thepredominance of charge carriers of at least one type are able to driftover a distance of greater than approximately 400 nm prior torecombining. The predominance of charge carriers of an embodimentincludes electrons. The predominance of charge carriers of an embodimentincludes holes.

Embodiments include a nanocrystal device in which a substantial portionof the flowing current is contributed from each of drift and diffusion.A substantial portion of the flowing current of the nanocrystal deviceof an embodiment is contributed from drift due to a field. A substantialportion of the flowing current of the nanocrystal device of anembodiment is contributed from diffusion due to a charge carrierconcentration gradient.

Embodiments include a region of a doped-nanocrystal nanocrystal devicewhich is substantially depleted of free carriers.

Embodiments include a region of an unbiased doped-nanocrystal devicewhich is substantially depleted of free carriers.

Embodiments are directed to an optoelectronic device comprising anintegrated circuit comprising a silicon substrate, at least onediffusion layer, at least one polysilicon layer and at least two metallayers, including at least a first metal layer and a second metal layer,an optically sensitive layer in electrical communication with the secondmetal layer; and the at least one polysilicon layer and the at least onediffusion layer forming a plurality of transistors in electricalcommunication with the optically sensitive layer through at least thesecond metal layer.

In this embodiment, the integrated circuit may a complementary metaloxide semiconductor (CMOS) integrated circuit. The minimum featurespacing of the integrated circuit is in a range of approximately 100 nmto 200 um. The at least two metal layers include metal interconnectlayers. The second metal layer forms contacts in electricalcommunication with the optically sensitive layer. The contacts comprisean aluminum body, a first coating and a second coating, the firstcoating comprising titanium nitride and positioned between the aluminumbody and the optically sensitive layer, the second coating comprisingtitanium oxynitride and positioned between the first coating and theoptically sensitive layer. The contacts comprise an aluminum body, afirst coating and a second coating, the first coating comprisingtitanium nitride and positioned between the aluminum body and theoptically sensitive layer, the second coating located between the firstcoating and the optically sensitive layer and comprising a metalselected from the group consisting of gold, platinum, palladium, nickeland tungsten. The contacts have a thickness less than approximately halfthe thickness of the first metal layer. The contacts have a thicknessless than approximately 50 nanometers and a width in a range ofapproximately 100 nm to 500 nm. The contacts have an aspect ratio ofthickness to width of at least 1:2 or 1:3 or 1:4. The contacts areformed from a plurality of metal sub-layers, each metal sub-layer havinga thickness of less than approximately 50 nm, each metal sub-layercomprising a constituent selected from the group consisting of titaniumnitride, titanium oxy nitride, gold, platinum, palladium, nickel andtungsten.

In one embodiment, the second metal layer consists of metal other thanaluminum, the metal including at least one layer selected from the groupconsisting of titanium nitride, titanium oxynitride, gold, platinum,palladium, nickel and tungsten; or the second metal layer consists ofmetal other than copper, the metal including at least one layer selectedfrom the group consisting of titanium nitride, titanium oxynitride,gold, platinum, palladium, nickel and tungsten; or the second metallayer comprises a constituent selected from the group consisting oftitanium nitride, titanium oxynitride, gold, platinum, palladium, nickeland tungsten. The optically sensitive layer makes direct contact withthe second metal layer. The optically sensitive layer comprises acoating on the second metal layer. The first metal layer has a thicknessin the range of approximately 100 nm to 500 nm. The metal layerscomprise at least one additional metal layer between the first metallayer and the second metal layer. Each of the first metal layer and theat least one additional metal layer comprises aluminum, wherein the atleast one additional metal layer excludes aluminum; or each of the firstmetal layer and the at least one additional metal layer comprisesaluminum and titanium nitride, wherein the at least one additional metallayer excludes aluminum. In one embodiment, each of the first metallayer and the at least one additional metal layer excludes aluminum; oreach of the first metal layer and the at least one additional metallayer excludes copper; or wherein the metal layers comprise at least twoadditional metal layers between the first metal layer and the secondmetal layer.

In an embodiment, the metal layers comprise at least three additionalmetal layers between the first metal layer and the second metal layer;or the metal layers comprise at least four additional metal layersbetween the first metal layer and the second metal layer. The firstmetal layer has a first thickness dimension and the second metal layerhas a second thickness dimension. The first thickness dimension may beless than the second thickness dimension, or the first thicknessdimension may be greater than the second thickness dimension. or thefirst thickness dimension is approximately equivalent to the secondthickness dimension. The first metal layer has a first aspect ratio andthe second metal layer has a second aspect ratio. The first aspect ratiomay be relatively high or relatively low. The second aspect ratio may berelatively high or relatively low, or the first aspect ratio isapproximately equivalent to the second aspect ratio.

In an embodiment, the integrated circuit results from 0.13 um CMOSprocessing. The integrated circuit results from 0.18 um CMOS processing.In an embodiment, a non-linear relationship exists between electricalcharacteristics of the optically sensitive layer and intensity of lightabsorbed by the optically sensitive layer, wherein a continuous functionrepresents the non-linear relationship. A rate of the current flowthrough the optically sensitive layer has a non-linear relationship withintensity of the light absorbed by the optically sensitive layer. Theoptically sensitive layer may have a non-linear relationship withintensity of the light absorbed by the optically sensitive layer. Theoptically sensitive layer has photoconductive gain when a voltagedifference is applied across the optically sensitive layer and theoptically sensitive layer is exposed to light.

In an embodiment, persistence of the optically sensitive layer isapproximately in a range of 1 ms to 200 ms. The optically sensitivelayer is a non-rectifying optically sensitive layer. The opticallysensitive layer has a surface area determined by a width dimension and alength dimension. The width dimension may be approximately 2 um or lessthan approximately 2 um, and the length dimension may be approximately 2um or less than approximately 2 um. The optically sensitive layer maycomprise a continuous film of interconnected nanocrystal particles. Thenanocrystal particles comprise a plurality of nanocrystal cores and ashell over the plurality of nanocrystal cores. The plurality ofnanocrystal cores may be fused. The physical proximity of thenanocrystal cores of adjacent nanocrystal particles provides electricalcommunication between the adjacent nanocrystal particles. The physicalproximity includes a separation distance of less than approximately 0.5nm.

In an embodiment, the electrical communication includes a hole mobilityof at least approximately 1E-5 square centimeter per volt-second acrossthe nanocrystal particles. The plurality of nanocrystal cores areelectrically interconnected with linker molecules. The linker moleculesinclude bidentate linker molecules. The linker molecules can includeethanedithiol or benzenedithiol.

In an embodiment, the optically sensitive layer comprises a unipolarphotoconductive layer including a first carrier type and a secondcarrier type, wherein a first mobility of the first carrier type ishigher than a second mobility of the second carrier type. The firstcarrier type is electrons and the second carrier type is holes, or thefirst carrier type is holes and the second carrier type is electrons.The optically sensitive layer comprises a nanocrystal material havingphotoconductive gain and a responsivity of at least approximately 0.4amps/volt (A/V). The responsivity is achieved under a bias approximatelyin a range of 0.5 volts to 5 volts.

The optically sensitive layer may comprise nanocrystals of a materialhaving a bulk bandgap, and wherein the nanocrystals are quantum confinedto have an effective bandgap more than twice the bulk bandgap; or theoptically sensitive layer includes nanocrystals comprisingnanoparticles, wherein a nanoparticle diameter of the nanoparticles isless than a Bohr exciton radius of bound electron-hole pairs within thenanoparticle. The optically sensitive layer comprises monodispersenanocrystals or nanocrystals. The nanocrystals are colloidal quantumdots. The quantum dots include a first carrier type and a second carriertype, wherein the first carrier type is a flowing carrier and the secondcarrier type is one of a substantially blocked carrier and a trappedcarrier. The colloidal quantum dots include organic ligands, wherein aflow of at least one of the first carrier type and the second carriertype is related to the organic ligands. The optically sensitive layercan be biased as both a current sink and a current source. The opticallysensitive layer comprises closely-packed semiconductor nanoparticlecores. Each core may be partially covered with an incomplete shell,where the shell produces trap states having substantially a single timeconstant. The nanoparticle cores comprise PbS partially covered with ashell comprising PbSO3. The nanoparticle cores are passivated usingligands of at least two substantially different lengths, or thenanoparticle cores are passivated using at least one ligand of at leastone length. The nanoparticle cores are passivated and crosslinked usingat least one crosslinking molecule of at least one length. Thecrosslinking molecule is a conductive crosslinker.

In an embodiment, each nanoparticle core is covered with a shell, wherethe shell comprises PbSO3, or the nanoparticle cores comprise PbS thatis partially oxidized and substantially lacking in PbSO4 (lead sulfate).The optically sensitive layer comprises a nanocrystalline solid, whereinat least a portion of a surface of the nanocrystalline solid isoxidized. A composition of the nanocrystalline solid excludes a firstset of native oxides and includes a second set of native oxides. Thefirst set of native oxides includes PbSO4 (lead sulfate) and the secondset of native oxides includes PbSO3.

In a device of an embodiment, trap states of the nanocrystalline solidprovide persistence, wherein an energy to escape from a predominant trapstate is less than or equal to approximately 0.1 eV. In the device, anon-predominant trap state, wherein an energy to escape from thenon-predominant trap state is greater than or equal to approximately 0.2eV. The device of comprises a continuous transparent layer, thecontinuous transparent layer comprising substantially transparentmaterial, wherein the continuous transparent layer at least partiallycovers the optically sensitive layer. An adhesion layer anchorsconstituents of the optically sensitive layer to circuitry of theintegrated circuit. The optically sensitive layer comprises at least oneof a wavelength-selective light-absorbing material and a photoconductivematerial. The device comprises an array of curved optical elements thatdetermine a distribution of intensity across the optically sensitivelayer. The optically sensitive layer comprises substantially fusednanocrystal cores having a dark current density less than approximately0.1 nA/cm2.

Embodiments are directed to an optoelectronic device comprising: anintegrated circuit comprising a silicon substrate, at least onediffusion layer, at least one polysilicon layer and at least two metallayers, including at least a first metal layer and a second metal layer,a coating on the second metal layer, the coating comprising an opticallysensitive layer in electrical communication with the second metal layer,the at least one polysilicon layer and the at least one diffusion layerforming a plurality of transistors in electrical communication with theoptically sensitive layer through at least the second metal layer.

Embodiments include an optoelectronic device comprising: an integratedcircuit comprising a silicon substrate, at least one diffusion layer, atleast one polysilicon layer and at least two metal layers, including atleast a first metal layer and a second metal layer, wherein the at leasttwo metal layers include metal interconnect layers; an opticallysensitive layer in electrical communication with the second metal layer;and the at least one polysilicon layer and the at least one diffusionlayer forming a plurality of transistors in electrical communicationwith the optically sensitive layer through at least the second metallayer.

Embodiments include an optoelectronic device comprising: an integratedcircuit comprising a silicon substrate, at least one diffusion layer, atleast one polysilicon layer and at least two metal layers, including atleast a first metal layer and a second metal layer, wherein theintegrated circuit is a complementary metal oxide semiconductor (CMOS)integrated circuit; an optically sensitive layer in electricalcommunication with the second metal layer; and the at least onepolysilicon layer and the at least one diffusion layer forming aplurality of transistors in electrical communication with the opticallysensitive layer through at least the second metal layer.

Embodiments include, an optoelectronic device comprising: an integratedcircuit comprising a silicon substrate, at least one diffusion layer, atleast one polysilicon layer and at least two metal layers, including atleast a first metal layer and a second metal layer; an opticallysensitive layer in electrical communication with the second metal layer,wherein the second metal layer forms contacts in electricalcommunication with the optically sensitive layer; and the at least onepolysilicon layer and the at least one diffusion layer forming aplurality of transistors in electrical communication with the opticallysensitive layer through at least the second metal layer.

Embodiments include an optoelectronic device comprising: an integratedcircuit comprising a silicon substrate, at least one diffusion layer, atleast one polysilicon layer and at least two metal layers, including atleast a first metal layer and a second metal layer; an opticallysensitive layer in electrical communication with the second metal layer,wherein the second metal layer forms contacts in electricalcommunication with the optically sensitive layer, wherein the contactscomprise an aluminum body, a first coating and a second coating; and theat least one polysilicon layer and the at least one diffusion layerforming a plurality of transistors in electrical communication with theoptically sensitive layer through at least the second metal layer.

Embodiments include an optoelectronic device comprising: an integratedcircuit comprising a silicon substrate, at least one diffusion layer, atleast one polysilicon layer and at least two metal layers, including atleast a first metal layer and a second metal layer; an opticallysensitive layer in electrical communication with the second metal layer,wherein the second metal layer forms contacts in electricalcommunication with the optically sensitive layer, wherein the contactscomprise an aluminum body, a first coating and a second coating, thefirst coating comprising titanium nitride and positioned between thealuminum body and the optically sensitive layer, the second coatingcomprising titanium oxynitride and positioned between the first coatingand the optically sensitive layer; and the at least one polysiliconlayer and the at least one diffusion layer forming a plurality oftransistors in electrical communication with the optically sensitivelayer through at least the second metal layer.

Embodiments include an optoelectronic device comprising: an integratedcircuit comprising a silicon substrate, at least one diffusion layer, atleast one polysilicon layer and at least two metal layers, including atleast a first metal layer and a second metal layer; an opticallysensitive layer in electrical communication with the second metal layer,wherein the second metal layer forms contacts in electricalcommunication with the optically sensitive layer, wherein the contactscomprise an aluminum body, a first coating and a second coating, thefirst coating comprising titanium nitride and positioned between thealuminum body and the optically sensitive layer, the second coatinglocated between the first coating and the optically sensitive layer andcomprising a metal selected from the group consisting of gold, platinum,palladium, nickel and tungsten; and the at least one polysilicon layerand the at least one diffusion layer forming a plurality of transistorsin electrical communication with the optically sensitive layer throughat least the second metal layer.

Embodiments include an optoelectronic device comprising:

an integrated circuit comprising a silicon substrate, at least onediffusion layer, at least one polysilicon layer and at least two metallayers, including at least a first metal layer and a second metal layer,the second metal layer comprising metal other than aluminum; anoptically sensitive layer in electrical communication with the secondmetal layer; and the at least one polysilicon layer and the at least onediffusion layer forming a plurality of transistors in electricalcommunication with the optically sensitive layer through at least thesecond metal layer.

Embodiments include an optoelectronic device comprising: an integratedcircuit comprising a silicon substrate, at least one diffusion layer, atleast one polysilicon layer and at least two metal layers, including atleast a first metal layer and a second metal layer, the second metallayer comprising metal other than copper; an optically sensitive layerin electrical communication with the second metal layer; and the atleast one polysilicon layer and the at least one diffusion layer forminga plurality of transistors in electrical communication with theoptically sensitive layer through at least the second metal layer.

Embodiments include an optoelectronic device comprising: an integratedcircuit comprising a silicon substrate, at least one diffusion layer, atleast one polysilicon layer and at least two metal layers, including atleast a first metal layer and a second metal layer, the second metallayer comprising a constituent selected from the group consisting oftitanium nitride, titanium oxynitride, gold, platinum, palladium, nickeland tungsten; an optically sensitive layer in electrical communicationwith the second metal layer; and the at least one polysilicon layer andthe at least one diffusion layer forming a plurality of transistors inelectrical communication with the optically sensitive layer through atleast the second metal layer.

Embodiments are directed to a method comprising: producing an integratedcircuit comprising a silicon substrate, at least one diffusion layer, atleast one polysilicon layer and at least two metal layers, including atleast a first metal layer and a second metal layer; producing anoptically sensitive layer in electrical communication with the secondmetal layer, wherein the at least one polysilicon layer and the at leastone diffusion layer form a plurality of transistors in electricalcommunication with the optically sensitive layer through at least thesecond metal layer.

Embodiments are directed to a method comprising: exposing an opticallysensitive material to light; providing a current flow through theoptically sensitive material, wherein a rate of the current flow throughthe optically sensitive material has a non-linear relationship withintensity of the light absorbed by the optically sensitive material;using the current flow to discharge a portion of charge from a chargestore over a period of time; and generating a signal from the chargestore based on the amount of charge remaining in the charge store afterthe period of time.

Embodiments are directed to a method comprising: exposing an opticallysensitive material to light; providing a current flow through theoptically sensitive material, the current flow varying with aphotoconductive gain of the optically sensitive material, wherein thephotoconductive gain during the exposing period depends on the intensityof the light absorbed by the optically sensitive material; using thecurrent flow to discharge a portion of charge from a charge store over aperiod of time; and generating a signal from the charge store based onthe amount of charge remaining in the charge store after the period oftime.

Embodiments are directed to a method comprising: exposing an opticallysensitive material to light; applying a voltage to the opticallysensitive material such that a voltage difference is formed across theoptically sensitive material; changing the voltage over a period of timeby flowing current through the optically sensitive material, wherein therate of the current flow through the optically sensitive material has anon-linear relationship with intensity of the light absorbed by theoptically sensitive material; and generating a signal based on thevoltage remaining after the period of time.

Embodiments are directed to a photodetector comprising: a pixel regioncomprising an optically sensitive material; pixel circuitry electricallycoupled to the optically sensitive material, the pixel circuitryestablishing a voltage over an integration period of time, wherein thevoltage has a non-linear relationship with intensity of light absorbedby the optically sensitive material of the respective pixel region,wherein a signal is generated based on the voltage after the integrationperiod of time, the signal having a noise level; a converter configuredto convert the signal into digital pixel data, wherein the converter hasan input range; and at least one of the pixel circuitry and theoptically sensitive layer providing a dynamic range more than at leasttwice the ratio of the input range of the converter divided by the noiselevel.

Embodiments include a photodetector comprising: a pixel regioncomprising an optically sensitive material; pixel circuitry inelectrical communication with the optically sensitive material, thepixel circuitry establishing a voltage over an integration period oftime, wherein the voltage has a non-linear relationship with intensityof light absorbed by the optically sensitive material of the respectivepixel region; read out circuitry configured to generate a signal basedon the voltage after the integration period of time; ananalog-to-digital converter configured to convert the signal intodigital pixel data, wherein the analog-to-digital converter has an inputrange and wherein the signal from the pixel circuitry has a noise level;and wherein the pixel circuitry and the optically sensitive layer areconfigured to provide a dynamic range more than at least twice the ratioof the input range of the analog-to-digital converter divided by thenoise level. The dynamic range is in a range of more than at least threetimes to approximately ten times the ratio of the input range divided bythe noise level. The dynamic range is more than at least three times theratio of the input range divided by the noise level. The dynamic rangemay be more than at least five or ten times the ratio of the input rangedivided by the noise level. The photodetector has a non-linearrelationship between electrical characteristics of the opticallysensitive material and intensity of light absorbed by the opticallysensitive material, wherein a continuous function represents thenon-linear relationship. The continuous function is a continuouspolynomial function representing the non-linear relationship betweenphotoconductive gain of the optically sensitive material and intensityof light absorbed by the optically sensitive material. A digital numbercorresponding to the digital pixel data has a linear relationship to theintensity.

Embodiments include an image sensor comprising: a photosensor arrayhaving a plurality of pixel regions, the pixel regions arranged into aplurality of rows and a plurality of columns, wherein each pixel regionincludes at least one optically sensitive material; pixel circuitrycoupled to each of the respective pixel regions, wherein the pixelcircuitry establishes a voltage over an integration period of time, thevoltage having a non-linear relationship with intensity of lightabsorbed by the optically sensitive material of the respective pixelregion, wherein output signals are generated based on the voltage; andsignal processing circuitry coupled to the pixel circuitry andgenerating pixel data for a subset of pixel regions using the respectiveoutput signals, wherein the pixel data has a linear relationship withthe intensity of the light absorbed by the optically sensitive materialof each of the respective pixel regions in the selected subset of pixelregions. The pixel circuitry comprises read out circuitry that generatesthe output signals. Pixel select circuitry configured to select thepixel circuitry for a subset of the pixel regions to be read out.

Embodiments include a photodetector comprising: a photosensor arrayhaving a plurality of pixel regions, the pixel regions arranged into aplurality of rows and a plurality of columns; each pixel regioncomprising at least one optically sensitive material; pixel circuitrycoupled to each of the respective pixel regions, wherein the pixelcircuitry establishes a voltage over an integration period of time, thevoltage having a non-linear relationship with intensity of lightabsorbed by the optically sensitive material of the respective pixelregion; the pixel circuitry including read out circuitry configured togenerate a signal based on the voltage; pixel select circuitryconfigured to select the pixel circuitry for a subset of the pixelregions to be read out; and signal processing circuitry configured togenerate digital pixel data for the selected subset of pixel regions,wherein the digital pixel data for the subset of pixel regions has alinear relationship with the intensity of the light absorbed by theoptically sensitive material of each of the respective pixel regions inthe selected subset of pixel regions.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material, wherein a non-linear relationship exists betweenelectrical characteristics of the optically sensitive material andintensity of light absorbed by the optically sensitive material, whereina continuous function represents the non-linear relationship; using thecurrent flow to discharge a portion of charge from a charge store over asingle integration period; and generating a signal from the charge storebased on the amount of charge remaining in the charge store after thesingle integration period. A non-linear relationship exists betweenphotoconductive gain of the optically sensitive material and intensityof light absorbed by the optically sensitive material. The continuousfunction is a continuous polynomial function representing the non-linearrelationship between photoconductive gain of the optically sensitivematerial and intensity of light absorbed by the optically sensitivematerial. A digital number output corresponding to the signal has alinear relationship to the intensity.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material; controlling a charge store over a single integrationperiod by discharging a portion of charge from the charge store inresponse to the current flow; and generating a data signal from thecharge store based on the amount of charge remaining after the singleintegration period; wherein a continuous function represents anon-linear relationship between photoconductive gain of the opticallysensitive material and intensity of light absorbed by the opticallysensitive material.

Embodiments include a photodetector comprising: a pixel regioncomprising an optically sensitive material; circuitry in electricalcommunication with the optically sensitive material, the circuitryestablishing a voltage using a single integration period of time for thepixel region, the circuitry generating a signal based on the voltageafter the single integration period of time, wherein the photoconductivegain of the optically sensitive material has a continuous functionalrelationship with intensity of the light absorbed by the opticallysensitive material; an analog-to-digital converter converting the signalinto digital pixel data, wherein the analog-to-digital converter has aninput range and wherein the signal from the pixel circuitry has a noiselevel; and wherein the pixel circuitry and the optically sensitive layerare configured to provide a dynamic range more than at least twice theratio of the input range of the analog-to-digital converter divided bythe noise level.

Embodiments include a photodetector comprising: a pixel regioncomprising an optically sensitive material having a non-linearrelationship between electrical characteristics of the opticallysensitive material and intensity of light absorbed by the opticallysensitive material circuitry in electrical communication with theoptically sensitive material, the circuitry establishing a voltage usinga single integration period of time for the pixel region, the circuitrygenerating a signal based on the voltage after the single integrationperiod of time, wherein the photoconductive gain of the opticallysensitive material has a continuous functional relationship withintensity of the light absorbed by the optically sensitive material; ananalog-to-digital converter converting the signal into digital pixeldata, wherein the analog-to-digital converter has an input range andwherein the signal from the pixel circuitry has a noise level; andwherein the pixel circuitry and the optically sensitive layer areconfigured to provide a dynamic range more than at least twice the ratioof the input range of the analog-to-digital converter divided by thenoise level.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material, wherein a rate of the current flow through theoptically sensitive material has a non-linear relationship withintensity of the light absorbed by the optically sensitive material;collecting charge from the current flow over a period of time; andgenerating a signal from the charge collected over the period of time.

Embodiments include a photodetector comprising: a pixel regioncomprising an optically sensitive material; pixel circuitry electricallycoupled to the optically sensitive material, the pixel circuitryproviding a current flow through the optically sensitive material,wherein a rate of the current flow through the optically sensitivematerial has a non-linear relationship with intensity of the lightabsorbed by the optically sensitive material; charge collectioncircuitry that collects charge relating to the current flow over aperiod of time; and read out circuitry that generates a signal from thecharge collected over the period of time. The photodetector has aconverter configured to convert the signal into digital pixel data,wherein the converter has an input range. At least one of the pixelcircuitry and the optically sensitive layer providing a dynamic rangemore than at least twice the ratio of the input range of the converterdivided by the noise level.

Embodiments include a photodetector comprising: a pixel regioncomprising an optically sensitive material; pixel circuitry electricallycoupled to the optically sensitive material, the pixel circuitryproviding a current flow through the optically sensitive material,wherein a rate of the current flow through the optically sensitivematerial has a non-linear relationship with intensity of the lightabsorbed by the optically sensitive material; charge collectioncircuitry that collects charge relating to the current flow over aperiod of time; and read out circuitry configured to generate a signalbased on the collected charge; an analog-to-digital converter configuredto convert the signal into digital pixel data, wherein theanalog-to-digital converter has an input range and wherein the signalfrom the pixel circuitry has a noise level; and wherein the pixelcircuitry and the optically sensitive layer are configured to provide adynamic range more than at least twice the ratio of the input range ofthe analog-to-digital converter divided by the noise level. The dynamicrange is in a range of more than at least three times to approximatelyten times the ratio of the input range divided by the noise level. Anon-linear relationship exists between electrical characteristics of theoptically sensitive material and intensity of light absorbed by theoptically sensitive material, wherein a continuous function representsthe non-linear relationship. The continuous function is a continuouspolynomial function representing the non-linear relationship. A digitalnumber corresponding to the digital pixel data has a linear relationshipto the intensity.

Embodiments include a photodetector comprising: a photosensor arrayhaving a plurality of pixel regions, the pixel regions arranged into aplurality of rows and a plurality of columns, wherein each pixel regionincludes at least one optically sensitive material; pixel circuitryelectrically coupled to the optically sensitive material, the pixelcircuitry providing a current flow through the optically sensitivematerial, wherein a rate of the current flow through the opticallysensitive material has a non-linear relationship with intensity of thelight absorbed by the optically sensitive material; signal processingcircuitry coupled to the pixel circuitry and generating pixel data for asubset of pixel regions using output signals of the respective pixelregions, wherein the pixel data has a linear relationship with theintensity of the light absorbed by the optically sensitive material ofeach of the respective pixel regions in the selected subset of pixelregions. The pixel circuitry comprises read out circuitry that generatesthe output signals.

Pixel select circuitry is configured to select the pixel circuitry for asubset of the pixel regions to be read out.

Embodiments include a photodetector comprising: a plurality ofelectrodes, including at least a first electrode and a second electrode;an optically sensitive material between the first electrode and thesecond electrode; circuitry that applies a voltage difference betweenthe first electrode and the second electrode such that current flowsthrough the optically sensitive material during an integration period oftime, wherein the rate of the current flow through the opticallysensitive material has a non-linear relationship with intensity of lightabsorbed by the optically sensitive material; a charge store inelectrical communication with at least one of the electrodes, thequantity of charge in the charge store based on the current flow throughthe optically sensitive material during the integration period of time;and read out circuitry configured to generate a signal based on thecharge in the charge store after the integration period of time. Aportion of the energy in the charge store is dissipated over theintegration period of time. The charge store is charged by the currentflow during the integration period of time.

Embodiments include a photodetector comprising: a photosensor arrayhaving a plurality of pixel regions, the pixel regions arranged into aplurality of rows and a plurality of columns; each pixel regioncomprising at least one optically sensitive material and a plurality ofelectrodes, including at least a first electrode and a second electrode;each pixel region comprising an optically sensitive material between thefirst electrode and the second electrode; pixel circuitry that applies avoltage difference between the first electrode and the second electrodesuch that current flows through the optically sensitive material duringan integration period of time, wherein the rate of the current flowthrough the optically sensitive material has a non-linear relationshipwith intensity of light absorbed by the optically sensitive material;the pixel circuitry including a charge store in electrical communicationwith at least one of the electrodes, the charge store storing energybased on the current flow through the optically sensitive materialduring the integration period of time; and read out circuitry configuredto generate a signal based on the energy of the charge store for therespective pixel region after the integration period of time; and pixelselect circuitry to select the pixel circuitry for a subset of the pixelregions to be read out.

Embodiments include a photodetector comprising: a photosensor arrayhaving a plurality of pixel regions, the pixel regions arranged into aplurality of rows and a plurality of columns; each pixel regioncomprising at least one optically sensitive material; pixel circuitryfor each of the respective pixel regions, the pixel circuitry for eachrespective pixel region applying a voltage difference across theoptically sensitive material for the respective pixel region, whereinthe rate of the current flow through the optically sensitive materialhas a non-linear relationship with intensity of light absorbed by theoptically sensitive material of the respective pixel region; the pixelcircuitry including a charge store to provide a charge related to thecurrent flow through the optically sensitive material of the respectivepixel region during the integration period of time; the pixel circuitryincluding read out circuitry to generate a signal based on the charge ofthe charge store for the respective pixel region after the integrationperiod of time; and pixel select circuitry to select the pixel circuitryfor a subset of the pixel regions to be read out. The pixel selectcircuitry selects the pixel circuitry for a subset of the pixel regionsto be read out nearly simultaneously.

Embodiments include a method comprising: providing an opticallysensitive material; causing a current to flow through the opticallysensitive material during an integration period of time by providing avoltage difference across the optically sensitive material and exposingthe optically sensitive material to light, wherein the rate of thecurrent flow through the optically sensitive material depends upon thevoltage difference across the optically sensitive material and intensityof the light absorbed by the optically sensitive material; using thecurrent flow through the optically sensitive material to discharge aportion of charge from a charge store during the integration period oftime; varying both the voltage difference across the optically sensitivematerial and the rate of the current flow through the opticallysensitive material during at least a portion of the integration periodwhile the intensity of the light substantially constant; and generatinga signal based on the amount of charge remaining in the charge storeafter the integration period of time.

Embodiments include a photodetector comprising: a pixel regioncomprising an optically sensitive material; pixel circuitry electricallycoupled to the optically sensitive material, the pixel circuitry causinga current to flow through the optically sensitive material during anintegration period of time by providing a voltage difference across theoptically sensitive material when the optically sensitive material isexposed to light, wherein the rate of the current flow through theoptically sensitive material depends upon the voltage difference acrossthe optically sensitive material and intensity of the light absorbed bythe optically sensitive material, wherein the current flow through theoptically sensitive material discharges a portion of charge from acharge store during the integration period of time, wherein both thevoltage difference across the optically sensitive material and the rateof the current flow through the optically sensitive material vary duringat least a portion of the integration period while the intensity of thelight is substantially constant; and read out circuitry generating asignal based on the amount of charge remaining in the charge store afterthe integration period of time.

Embodiments include a method comprising: providing an opticallysensitive material; causing a current to flow through the opticallysensitive material during an integration period of time by providing avoltage difference across the optically sensitive material and exposingthe optically sensitive material to light, wherein the rate of thecurrent flow through the optically sensitive material depends upon thevoltage difference across the optically sensitive material and intensityof the light absorbed by the optically sensitive material; collectingcharge from the current flow during the integration period of time;varying both the voltage difference across the optically sensitivematerial and the rate of the current flow through the opticallysensitive material during at least a portion of the integration periodwhile maintaining the intensity of the light substantially constant; andgenerating a signal based on the charge collected during the integrationperiod of time.

Embodiments include a photodetector comprising: a pixel regioncomprising an optically sensitive material; pixel circuitry electricallycoupled to the optically sensitive material, the pixel circuitry causinga current to flow through the optically sensitive material during anintegration period of time by providing a voltage difference across theoptically sensitive material when the optically sensitive material isexposed to light, wherein the rate of the current flow through theoptically sensitive material depends upon the voltage difference acrossthe optically sensitive material and intensity of the light absorbed bythe optically sensitive material; the pixel circuitry collecting chargefrom the current flow during the integration period of time, whereinboth the voltage difference across the optically sensitive material andthe rate of the current flow through the optically sensitive materialvary during at least a portion of the integration period whilemaintaining the intensity of the light substantially constant; and readout circuitry generating a signal based on the charge collected duringthe integration period of time.

Embodiments include a photodetector comprising: a plurality ofelectrodes, including at least a first electrode and a second electrode;an optically sensitive material between the first electrode and thesecond electrode; circuitry configured to apply a voltage differencebetween the first electrode and the second electrode such that currentflows through the optically sensitive material during an integrationperiod of time, wherein the rate of the current flow through theoptically sensitive material depends upon the voltage difference acrossthe optically sensitive material and an intensity of light absorbed bythe optically sensitive material; the circuitry configured to vary boththe voltage difference across the optically sensitive material and therate of the current flow through the optically sensitive material for aconstant intensity of light during at least a portion of the integrationperiod; a charge store in electrical communication with at least one ofthe electrodes, the charge store configured to provide a chargeresponsive to the current flow through the optically sensitive materialduring the integration period of time; and read out circuitry configuredto generate a signal based on the charge of the charge store after theintegration period of time.

Embodiments include a photodetector comprising: a photosensor arrayhaving a plurality of pixel regions, the pixel regions arranged into aplurality of rows and a plurality of columns; each pixel regioncomprising at least one optically sensitive material; pixel circuitryfor each of the respective pixel regions, the pixel circuitry for eachrespective pixel region configured to apply a voltage difference acrossthe optically sensitive material for the respective pixel region,wherein the rate of the current flow through the optically sensitivematerial depends upon the voltage difference across the opticallysensitive material and an intensity of light absorbed by the opticallysensitive material of the respective pixel region; the pixel circuitryconfigured to vary both the voltage difference across the opticallysensitive material and the rate of the current flow through theoptically sensitive material for a constant intensity of light during atleast a portion of the integration period; the pixel circuitry includinga charge store, the charge store configured to provide a charge inresponse to the current flow through the optically sensitive material ofthe respective pixel region during the integration period of time; thepixel circuitry including read out circuitry configured to generate asignal based on the charge of the charge store for the respective pixelregion after the integration period of time; and pixel select circuitryconfigured to select the pixel circuitry for a subset of the pixelregions to be read out.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material, wherein optical sensitivity of the opticallysensitive material depends upon intensity of light absorbed by theoptically sensitive material; using the current flow to discharge aportion of charge from a charge store over a period of time; andgenerating a signal from the charge store based on the amount of chargeremaining in the charge store after the period of time. The opticalsensitivity of the optically sensitive material at an intensity of lightless than approximately 1 lux is more than twice the optical sensitivityof the optically sensitive material at an intensity of light of at least100 lux; or the optical sensitivity of the optically sensitive materialat an intensity of light less than approximately 1 lux is more than tentimes the optical sensitivity of the optically sensitive material at anintensity of light of at least 100 lux.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material, the current flow varying with a photoconductive gainof the optically sensitive material, wherein optical sensitivity of theoptically sensitive material depends upon intensity of light absorbed bythe optically sensitive material; using the current flow to discharge aportion of charge from a charge store over a period of time; andgenerating a signal from the charge store based on the amount of chargeremaining in the charge store after the period of time.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; applying a voltage to the optically sensitivematerial such that a voltage difference is formed across the opticallysensitive material; changing the voltage over a period of time byflowing current through the optically sensitive material, whereinoptical sensitivity of the optically sensitive material depends uponintensity of light absorbed by the optically sensitive material; andgenerating a signal based on the voltage remaining after the period oftime.

Embodiments include a photodetector comprising: a pixel regioncomprising an optically sensitive material, wherein optical sensitivityof the optically sensitive material depends upon intensity of lightabsorbed by the optically sensitive material; pixel circuitryelectrically coupled to the optically sensitive material, the pixelcircuitry establishing a voltage over an integration period of time,wherein a signal is generated based on the voltage after the integrationperiod of time, the signal having a noise level; a converter configuredto convert the signal into digital pixel data, wherein the converter hasan input range; and at least one of the pixel circuitry and theoptically sensitive layer providing a dynamic range more than at leasttwice the ratio of the input range of the converter divided by the noiselevel. The voltage has a non-linear relationship with intensity of lightabsorbed by the optically sensitive material of the respective pixelregion.

Embodiments include a photodetector comprising: a pixel regioncomprising an optically sensitive material, wherein optical sensitivityof the optically sensitive material depends upon intensity of lightabsorbed by the optically sensitive material; pixel circuitry inelectrical communication with the optically sensitive material, thepixel circuitry establishing a voltage over an integration period oftime; read out circuitry configured to generate a signal based on thevoltage after the integration period of time; an analog-to-digitalconverter configured to convert the signal into digital pixel data,wherein the analog-to-digital converter has an input range and whereinthe signal from the pixel circuitry has a noise level; and wherein thepixel circuitry and the optically sensitive layer are configured toprovide a dynamic range more than at least twice the ratio of the inputrange of the analog-to-digital converter divided by the noise level. Thevoltage has a non-linear relationship with intensity of light absorbedby the optically sensitive material of the respective pixel region. Thedynamic range is in a range of more than at least three times toapproximately ten times the ratio of the input range divided by thenoise level, or it is more than at least three times the ratio of theinput range divided by the noise level, or it is more than at least fivetimes the ratio of the input range divided by the noise level, or it ismore than at least ten times the ratio of the input range divided by thenoise level. A non-linear relationship exists between electricalcharacteristics of the optically sensitive material and intensity oflight absorbed by the optically sensitive material, wherein a continuousfunction represents the non-linear relationship. The continuous functionis a continuous polynomial function representing the non-linearrelationship between photoconductive gain of the optically sensitivematerial and intensity of light absorbed by the optically sensitivematerial. A digital number corresponding to the digital pixel data has alinear relationship to the intensity.

Embodiments include a photodetector comprising: a photosensor arrayhaving a plurality of pixel regions, the pixel regions arranged into aplurality of rows and a plurality of columns, wherein each pixel regionincludes at least one optically sensitive material, wherein opticalsensitivity of the optically sensitive material depends upon intensityof light absorbed by the optically sensitive material; pixel circuitrycoupled to each of the respective pixel regions, wherein the pixelcircuitry establishes a voltage over an integration period of time,wherein output signals are generated based on the voltage; and signalprocessing circuitry coupled to the pixel circuitry and generating pixeldata for a subset of pixel regions using the respective output signals,wherein the pixel data has a linear relationship with the intensity ofthe light absorbed by the optically sensitive material of each of therespective pixel regions in the selected subset of pixel regions. Thevoltage has a non-linear relationship with intensity of light absorbedby the optically sensitive material of the respective pixel region. Thepixel circuitry comprises read out circuitry that generates the outputsignals. The pixel select circuitry selects the pixel circuitry for asubset of the pixel regions to be read out.

Embodiments include a photodetector comprising: a photosensor arrayhaving a plurality of pixel regions, the pixel regions arranged into aplurality of rows and a plurality of columns; each pixel regioncomprising at least one optically sensitive material, wherein opticalsensitivity of the optically sensitive material depends upon intensityof light absorbed by the optically sensitive material; pixel circuitrycoupled to each of the respective pixel regions, wherein the pixelcircuitry establishes a voltage over an integration period of time; thepixel circuitry including read out circuitry configured to generate asignal based on the voltage; pixel select circuitry configured to selectthe pixel circuitry for a subset of the pixel regions to be read out;and signal processing circuitry configured to generate digital pixeldata for the selected subset of pixel regions, wherein the digital pixeldata for the subset of pixel regions has a linear relationship with theintensity of the light absorbed by the optically sensitive material ofeach of the respective pixel regions in the selected subset of pixelregions. The voltage has a non-linear relationship with intensity oflight absorbed by the optically sensitive material of the respectivepixel region.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material, wherein the rate of the current flow through theoptically sensitive material varies with optical sensitivity of theoptically sensitive material, wherein optical sensitivity depends uponintensity of light absorbed by the optically sensitive material;collecting charge from the current flow over a period of time; andgenerating a signal from the charge collected over the period of time.The optical sensitivity is more than 1000 mV/lux-s at relatively lowlight levels and less than 500 mV/lux-s at relatively high light levels,or it is more than 2000 mV/lux-s at relatively low light levels and lessthan 400 mV/lux-s at relatively high light levels, or it is more than3000 mV/lux-s at relatively low light levels and less than 300 mV/lux-sat relatively high light levels.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material, wherein the rate of the current flow through theoptically sensitive material varies with optical sensitivity of theoptically sensitive material, wherein the optical sensitivity at anintensity of light less than approximately 1 lux is more than twice theoptical sensitivity at an intensity of light of at least 100 lux;collecting charge from the current flow over a period of time; andgenerating a signal from the charge collected over the period of time.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material, wherein the rate of the current flow through theoptically sensitive material varies with optical sensitivity of theoptically sensitive material, wherein the optical sensitivity at anintensity of light less than approximately 1 lux is more than ten timesthe optical sensitivity at an intensity of light of at least 100 lux;collecting charge from the current flow over a period of time; andgenerating a signal from the charge collected over the period of time.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material, wherein the rate of the current flow through theoptically sensitive material varies with optical sensitivity of theoptically sensitive material, wherein the optical sensitivity is morethan 600 mV/lux-s at an intensity of light less than 1 lux and theoptical sensitivity is more than 600 mV/lux-s at an intensity of lightof at least 100 lux; collecting charge from the current flow over aperiod of time; and generating a signal from the charge collected overthe period of time.

Embodiments include a photodetector comprising: a plurality ofelectrodes, including at least a first electrode and a second electrode;an optically sensitive material between the first electrode and thesecond electrode; circuitry that applies a voltage difference betweenthe first electrode and the second electrode such that current flowsthrough the optically sensitive material during an integration period oftime, wherein optical sensitivity of the optically sensitive materialdepends upon intensity of light absorbed by the optically sensitivematerial; a charge store in electrical communication with at least oneof the electrodes, the charge store storing energy based on the currentflow through the optically sensitive material during the integrationperiod of time; and read out circuitry configured to generate a signalbased on the energy of the charge store after the integration period oftime. A portion of the energy in the charge store is dissipated over theintegration period of time. The charge store is charged by the currentflow during the integration period of time. A rate of the current flowthrough the optically sensitive material has a non-linear relationshipwith intensity of light absorbed by the optically sensitive material.

Embodiments include a photodetector comprising: a photosensor arrayhaving a plurality of pixel regions, the pixel regions arranged into aplurality of rows and a plurality of columns; each pixel regioncomprising at least one optically sensitive material; pixel circuitryfor each of the respective pixel regions, the pixel circuitry for eachrespective pixel region applying a voltage difference across theoptically sensitive material for the respective pixel region, whereinoptical sensitivity of the optically sensitive material depends uponintensity of light absorbed by the optically sensitive material; thepixel circuitry including a charge store to provide a charge related tothe current flow through the optically sensitive material of therespective pixel region during the integration period of time; the pixelcircuitry including read out circuitry to generate a signal based on thecharge of the charge store for the respective pixel region after theintegration period of time; and pixel select circuitry to select thepixel circuitry for a subset of the pixel regions to be read out. A rateof the current flow through the optically sensitive material has anon-linear relationship with intensity of light absorbed by theoptically sensitive material of the respective pixel region.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material; using the current flow to discharge a portion ofstored charge from a charge store over a period of time; generating asignal from the charge store based on the amount of charge remaining inthe charge store after the period of time; wherein a rate of the currentflow through the optically sensitive material at relatively high lightlevels maintains the stored charge above a minimum threshold as a resultof a non-linear relationship between the current flow and intensity ofthe light absorbed by the optically sensitive material, whereingenerating of the signal occurs when the stored charge is greater thanthe minimum threshold.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material; using the current flow to discharge a portion ofstored charge from a charge store over a period of time; generating asignal from the charge store based on the amount of charge remaining inthe charge store after the period of time; wherein a rate of the currentflow through the optically sensitive material at relatively high lightlevels causes the stored charge to remain above a minimum threshold as aresult of a non-linear relationship between the current flow andintensity of the light absorbed by the optically sensitive material,wherein generating of the signal occurs when the stored charge isgreater than the minimum threshold.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material; using the current flow to discharge a portion ofstored charge from a charge store over a period of time; generating asignal from the charge store based on the amount of charge remaining inthe charge store after the period of time; wherein a rate of the currentflow through the optically sensitive material at relatively high lightlevels controls the discharge so that stored charge in the charge storeremains above a minimum threshold as a result of a non-linearrelationship between the current flow and intensity of the lightabsorbed by the optically sensitive material, wherein generating of thesignal occurs when the charge stored is greater than the minimumthreshold. The rate of current flow is non-linear relative to lightintensity such that the optical sensitivity of the optically sensitivematerial at 1 lux is more than twice the optical sensitivity at 100 lux.The rate of current flow is non-linear relative to light intensity suchthat the dynamic range of the optically sensitive material is greaterthan dynamic range of an optical material in which the opticalsensitivity at 1 lux is substantially the same as the opticalsensitivity at 100 lux.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material, the current flow varying with a photoconductive gainof the optically sensitive material; using the current flow to dischargea portion of charge from a charge store over a period of time;generating a signal from the charge store based on the amount of chargeremaining in the charge store after the period of time; wherein a rateof the current flow through the optically sensitive material atrelatively high light levels causes the charge in the charge store toremain above a minimum threshold as a result of a non-linearrelationship between the photoconductive gain of the optically sensitivematerial and intensity of the light absorbed by the optically sensitivematerial, wherein generating of the signal occurs when the stored chargeis greater than the minimum threshold.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material, the current flow varying with a photoconductive gainof the optically sensitive material; using the current flow to dischargea portion of charge from a charge store over a period of time;generating a signal from the charge store based on the amount of chargeremaining in the charge store after the period of time; wherein a rateof the current flow through the optically sensitive material atrelatively high light levels controls the discharge so that storedcharge in the charge store remains above a minimum threshold as a resultof a non-linear relationship between the current flow and intensity ofthe light absorbed by the optically sensitive material, whereingenerating of the signal occurs when the charge stored is greater thanthe minimum threshold.

Embodiments include a photodetector comprising: a pixel regioncomprising an optically sensitive material; pixel circuitry electricallycoupled to the optically sensitive material, the pixel circuitryestablishing a voltage over an integration period of time, wherein asignal is generated based on the voltage after the integration period oftime, the signal having a noise level; wherein a rate of the currentflow through the optically sensitive material at relatively high lightlevels causes the voltage to remain above a minimum threshold as aresult of a non-linear relationship between the voltage and intensity ofthe light absorbed by the optically sensitive material of the respectivepixel region, wherein generating of the signal occurs when the voltageis greater than the minimum threshold; a converter configured to convertthe signal into digital pixel data, wherein the converter has an inputrange; and at least one of the pixel circuitry and the opticallysensitive layer providing a dynamic range more than at least twice theratio of the input range of the converter divided by the noise level.The rate of current flow is non-linear relative to light intensity suchthat the optical sensitivity of the optically sensitive material at 1lux is more than twice the optical sensitivity at 100 lux. The rate ofcurrent flow is non-linear relative to light intensity such that thedynamic range of the optically sensitive material is greater thandynamic range of an optical material in which the optical sensitivity at1 lux is substantially the same as the optical sensitivity at 100 lux.

Embodiments include a photodetector comprising: a pixel regioncomprising an optically sensitive material; pixel circuitry inelectrical communication with the optically sensitive material, thepixel circuitry establishing a voltage over an integration period oftime; read out circuitry configured to generate a signal based on thevoltage after the integration period of time, wherein a rate of thecurrent flow through the optically sensitive material at relatively highlight levels causes the voltage to remain above a minimum threshold as aresult of a non-linear relationship between the voltage and intensity ofthe light absorbed by the optically sensitive material, whereingenerating of the signal occurs when the voltage is greater than theminimum threshold; an analog-to-digital converter configured to convertthe signal into digital pixel data, wherein the analog-to-digitalconverter has an input range and wherein the signal from the pixelcircuitry has a noise level; and wherein the pixel circuitry and theoptically sensitive layer are configured to provide a dynamic range morethan at least twice the ratio of the input range of theanalog-to-digital converter divided by the noise level. The dynamicrange is in a range of more than at least three times to approximatelyten times the ratio of the input range divided by the noise level. Thedynamic range is more than at least three times the ratio of the inputrange divided by the noise level, or it is more than at least five timesthe ratio of the input range divided by the noise level, or it is morethan at least ten times the ratio of the input range divided by thenoise level. A non-linear relationship exists between electricalcharacteristics of the optically sensitive material and intensity oflight absorbed by the optically sensitive material, wherein a continuousfunction represents the non-linear relationship. The continuous functionis a continuous polynomial function representing the non-linearrelationship between photoconductive gain of the optically sensitivematerial and intensity of light absorbed by the optically sensitivematerial. A digital number corresponding to the digital pixel data has alinear relationship to the intensity. The rate of current flow isnon-linear relative to light intensity such that the optical sensitivityof the optically sensitive material at 1 lux is more than twice theoptical sensitivity at 100 lux. The rate of current flow is non-linearrelative to light intensity such that the dynamic range of the opticallysensitive material is greater than dynamic range of an optical materialin which the optical sensitivity at 1 lux is substantially the same asthe optical sensitivity at 100 lux.

Embodiments include a photodetector comprising: a photosensor arrayhaving a plurality of pixel regions, the pixel regions arranged into aplurality of rows and a plurality of columns, wherein each pixel regionincludes at least one optically sensitive material; pixel circuitrycoupled to each of the respective pixel regions, wherein the pixelcircuitry establishes a voltage over an integration period of time,wherein output signals are generated based on the voltage, wherein arate of the current flow through the optically sensitive material atrelatively high light levels causes the voltage to remain above aminimum threshold as a result of a non-linear relationship between thevoltage and intensity of the light absorbed by the optically sensitivematerial, wherein generating of the output signals occurs when thevoltage is greater than the minimum threshold; and signal processingcircuitry coupled to the pixel circuitry and generating pixel data for asubset of pixel regions using the respective output signals, wherein thepixel data has a linear relationship with the intensity of the lightabsorbed by the optically sensitive material of each of the respectivepixel regions in the selected subset of pixel regions. The pixelcircuitry comprises read out circuitry that generates the outputsignals. The pixel select circuitry configured to select the pixelcircuitry for a subset of the pixel regions to be read out.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; providing a current flow through the opticallysensitive material; collecting charge from the current flow over aperiod of time; generating a signal from the charge collected over theperiod of time; wherein a rate of the current flow through the opticallysensitive material at relatively high light levels causes collectedcharge to remain above a minimum threshold as a result of a non-linearrelationship between the current flow and intensity of the lightabsorbed by the optically sensitive material, wherein generating of thesignal occurs when the collected charge is greater than the minimumthreshold. The rate of current flow is non-linear relative to lightintensity such that the optical sensitivity of the optically sensitivematerial at 1 lux is more than twice the optical sensitivity at 100 lux.The rate of current flow is non-linear relative to light intensity suchthat the dynamic range of the optically sensitive material is greaterthan dynamic range of an optical material in which the opticalsensitivity at 1 lux is substantially the same as the opticalsensitivity at 100 lux.

Embodiments include a photodetector comprising: a plurality ofelectrodes, including at least a first electrode and a second electrode;an optically sensitive material between the first electrode and thesecond electrode; circuitry that applies a voltage difference betweenthe first electrode and the second electrode such that current flowsthrough the optically sensitive material during an integration period oftime; a charge store in electrical communication with at least one ofthe electrodes, the charge store storing energy based on the currentflow through the optically sensitive material during the integrationperiod of time; and read out circuitry configured to generate a signalbased on the energy of the charge store after the integration period oftime; wherein a rate of the current flow through the optically sensitivematerial at relatively high light levels causes the stored energy toremain above a minimum threshold as a result of a non-linearrelationship between the current flow and intensity of the lightabsorbed by the optically sensitive material, wherein generating of thesignal occurs when the stored energy is greater than the minimumthreshold. A portion of the energy in the charge store is dissipatedover the integration period of time. The charge store is charged by thecurrent flow during the integration period of time. The read outcircuitry is configured such that there is a minimum voltage level thatcan be read from the charge store. The charge store is reset to a firstvoltage level at the beginning of the integration period of time. therate of current flow is non-linear relative to light intensity such thatthe optical sensitivity of the optically sensitive material at 1 lux ismore than twice the optical sensitivity at 100 lux. The rate of currentflow is non-linear relative to light intensity such that the dynamicrange of the optically sensitive material is greater than dynamic rangeof an optical material in which the optical sensitivity at 1 lux issubstantially the same as the optical sensitivity at 100 lux.

Embodiments include a photodetector comprising: a photosensor arrayhaving a plurality of pixel regions, the pixel regions arranged into aplurality of rows and a plurality of columns; each pixel regioncomprising at least one optically sensitive material; pixel circuitryfor each of the respective pixel regions, the pixel circuitry for eachrespective pixel region applying a voltage difference across theoptically sensitive material for the respective pixel region; the pixelcircuitry including a charge store to provide a charge related to thecurrent flow through the optically sensitive material of the respectivepixel region during an integration period of time; the pixel circuitryincluding read out circuitry to generate a signal based on the charge ofthe charge store for the respective pixel region after the integrationperiod of time; and pixel select circuitry to select the pixel circuitryfor a subset of the pixel regions to be read out; wherein a rate of thecurrent flow through the optically sensitive material at relatively highlight levels causes the stored charge to remain above a minimumthreshold as a result of a non-linear relationship between the currentflow and intensity of the light absorbed by the optically sensitivematerial, wherein generating of the signal occurs when the stored chargeis greater than the minimum threshold. The read out circuitry isconfigured such that there is a minimum voltage level that can be readfrom the charge store. The charge store is reset to a first voltagelevel at the beginning of the integration period of time. The rate ofcurrent flow is non-linear relative to light intensity such that theoptical sensitivity of the optically sensitive material at 1 lux is morethan twice the optical sensitivity at 100 lux. The rate of current flowis non-linear relative to light intensity such that the dynamic range ofthe optically sensitive material is greater than dynamic range of anoptical material in which the optical sensitivity at 1 lux issubstantially the same as the optical sensitivity at 100 lux.

Embodiments include a photodetector comprising: a semiconductorsubstrate;

a photosensor array having a plurality of pixel regions, the pixelregions arranged into a plurality of rows and a plurality of columns;each pixel region comprising at least one optically sensitive materialover a portion of the semiconductor substrate; pixel circuitry formed onthe semiconductor substrate for each of the respective pixel regions,the pixel circuitry for each respective pixel region configured to applya voltage difference across the optically sensitive material for therespective pixel region and to read out a signal based on a flow ofcurrent through the optically sensitive material over a period of time;and at least a portion of the pixel circuitry for a first respectivepixel region formed under the optically sensitive material for adifferent respective pixel region that is not read out by the pixelcircuitry for the first respective pixel region. The pixel circuitry forthe first respective pixel region includes a plurality of circuitelements, wherein at least one circuit element is formed under both theoptically sensitive material for the first respective pixel region andoptically sensitive material for the different respective pixel region.The first pixel circuitry for the first respective pixel region isformed in a first half of a first region of the semiconductor substrateand a first half of a second region of the semiconductor substrate,wherein second pixel circuitry for a second respective pixel region isformed in a second half of the first region of the semiconductorsubstrate and a second half of the second region of the semiconductorsubstrate. The first region forms a first rectangular region on thesemiconductor substrate and the second region forms a second rectangularregion on the semiconductor substrate, wherein a first size of the firstregion and a first size of the second region are related by a firstaspect ratio. The first aspect ratio is 1:1, or 2:3, or 3:4. The firstpixel circuitry is substantially contained in a third rectangular regionand the second pixel circuitry is substantially contained in a fourthrectangular region, wherein a third size of the third rectangular regionand a fourth size of the fourth rectangular region are related by asecond aspect ratio. The second aspect ratio is higher than the firstaspect ratio, and may be more than two times the first aspect ratio.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a photosensor array having a plurality of pixel regions, thepixel regions arranged into a plurality of rows and a plurality ofcolumns; each pixel region comprising at least one optically sensitivematerial over a portion of the semiconductor substrate; pixel circuitryformed on the semiconductor substrate for each of the respective pixelregions, the pixel circuitry for each respective pixel region configuredto apply a voltage difference across the optically sensitive materialfor the respective pixel region and to read out a signal based on alevel of light intensity absorbed by the optically sensitive layer forthe respective pixel region; and at least a portion of the pixelcircuitry for a first respective pixel region formed under the opticallysensitive material for a different respective pixel region that is notread out by the pixel circuitry for the first respective pixel region.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a photosensor array having a plurality of pixel regions, thepixel regions arranged into a plurality of rows and a plurality ofcolumns and including at least a first pixel region adjacent to a secondpixel region; each pixel region comprising at least one opticallysensitive material over a portion of the semiconductor substrate,wherein the optically sensitive material for the first pixel region isover a first portion of the semiconductor substrate and the sensitivematerial for the second pixel region is over a second portion of thesemiconductor substrate; and pixel circuitry formed on the semiconductorsubstrate for each of the respective pixel regions, the pixel circuitryfor each respective pixel region configured to apply a voltagedifference across the optically sensitive material for the respectivepixel region and to read out a signal based on a flow of current throughthe optically sensitive material over a period of time; wherein thepixel circuitry for the first pixel region extends from the firstportion of the semiconductor substrate to the second portion of thesemiconductor substrate and the pixel circuitry for the second pixelregion extends from the second portion of the semiconductor substrate tothe first portion of the semiconductor substrate.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a photosensor array having a plurality of pixel regions, thepixel regions arranged into a plurality of rows and a plurality ofcolumns and including at least a first pixel region adjacent to a secondpixel region; each pixel region comprising at least one opticallysensitive material over a portion of the semiconductor substrate,wherein the optically sensitive material for the first pixel region isover a first portion of the semiconductor substrate and the sensitivematerial for the second pixel region is over a second portion of thesemiconductor substrate; and pixel circuitry formed on the semiconductorsubstrate for each of the respective pixel regions, the pixel circuitryfor each respective pixel region configured to apply a voltagedifference across the optically sensitive material for the respectivepixel region and to read out a signal based on a level of lightintensity absorbed by the optically sensitive layer for the respectivepixel region; wherein the pixel circuitry for the first pixel regionextends from the first portion of the semiconductor substrate to thesecond portion of the semiconductor substrate and the pixel circuitryfor the second pixel region extends from the second portion of thesemiconductor substrate to the first portion of the semiconductorsubstrate. The pixel region includes a vertical stacked pixel, thevertical stacked pixel comprising at least two optically sensitivelayers, a first optically sensitive layer and a second opticallysensitive layer, the first optically sensitive layer over at least aportion of an integrated circuit and the second optically sensitivelayer over the first optically sensitive layer. The integrated circuitincludes at least a portion of the pixel circuitry. The opticallysensitive layers can be configured as a current source or as a currentsink. The pixel circuitry includes a charge store that is a storageelement, wherein the charge store is coupled to the optically sensitivelayers and establishes the voltage. The charge store is independent fromthe optically sensitive layers and isolated from a source of the light.The charge store is bound by the integrated circuit. The charge storecan be a capacitor, or parasitic capacitance. The pixel circuitryincludes a reset mechanism coupled to the optically sensitive layers.The reset mechanism resets the optically sensitive layers independent ofthe charge store. The pixel circuitry comprises a separation elementcoupled between the optically sensitive layers and the charge store. Theseparation element includes a non-linear element. The separation elementcan include a diode or a switch. The pixel circuitry includes a readoutelement, the readout element coupled to the optically sensitive layersand operating independently of common connected devices of the pixelcircuitry and the optically sensitive material. The readout element is atransistor, and may operate as an amplifier, and the amplifier operatesmay operate as a source follower. The pixel circuitry may include atleast one diode coupled to the optically sensitive layers. The diode canbe an implicit diode, or a parasitic diode, and the diode may reset theoptically sensitive material, or control the readout element.

The photodetector of an embodiment may comprise two electrodes, whereineach optically sensitive layer is interposed between the two electrodes,the electrodes including a respective first electrode and a respectivesecond electrode. The respective first electrode and second electrodefor the first optically sensitive layer are different electrodes thanthe respective first electrode and second electrode for the secondoptically sensitive layer. The respective first electrode for the firstoptically sensitive layer is a different electrode than the respectivefirst electrode for the second optically sensitive layer. The secondrespective electrode for the second optically sensitive layer is acommon electrode common to both the first optically sensitive layer andthe second optically sensitive layer. The common electrode extendsvertically from the first optically sensitive layer to the secondoptically sensitive layer. The common electrode extends vertically fromthe integrated circuit along a portion of the first optically sensitivelayer and the second optically sensitive layer. The common electrode iscoupled to a dynamic signaling component. The pixel region comprises aplurality of vertical stacked pixels, each of the plurality of verticalstacked pixels comprising at least two optically sensitive layers, arespective first optically sensitive layer and a respective secondoptically sensitive layer, the respective first optically sensitivelayer over at least a portion of the integrated circuit and therespective second optically sensitive layer over the respective firstoptically sensitive layer. Each optically sensitive layer is interposedbetween two electrodes, the electrodes including a respective firstelectrode and a respective second electrode, wherein the integratedcircuit is coupled to the electrodes and selectively applies a bias tothe electrodes and reads signals from the optically sensitive layers,wherein the signals are related to the number of photons received by therespective optically sensitive layer. The second respective electrodefor the second optically sensitive layer is a common electrode common tothe respective second optically sensitive layer of the plurality ofvertical stacked pixels. The respective second electrode as the commonelectrode comprises a mesh between at least two adjacent verticalstacked pixels of the plurality of vertical stacked pixels. At least aportion of the pixel circuitry for a first vertical stacked pixel isformed under the optically sensitive material for a second verticalstacked pixel that is not read out by the pixel circuitry for the firstvertical stacked pixel. Each respective first electrode is in contactwith the respective first optically sensitive layer, and each respectivesecond electrode is in contact with the respective second opticallysensitive layer. Each respective first electrode is positioned laterallyrelative to at least a portion of the respective second electrode, atleast a portion of each respective second electrode is on the same layerof the integrated circuit as the respective first electrode and therespective optically sensitive layer. The respective second electrodefor the first optically sensitive layer and the second opticallysensitive layer comprises a common electrode disposed around the firstelectrode. The second electrode is at least partially transparent and ispositioned over the respective optically sensitive layer. The respectivefirst electrode and the respective second electrode are non-transparentand separated by a distance corresponding to a width dimension and alength dimension. The width dimension is approximately 2 um, and thelength dimension is approximately 2 um; or the width dimension is lessthan approximately 2 um, and the length dimension is less thanapproximately 2 um. At least one of the optically sensitive layerscomprises monodisperse nanocrystals. Each of the optically sensitivelayers comprises nanocrystals of different materials.

The photodetector of this embodiment may have the first opticallysensitive layer including a first material having a first bulk bandgapand the second optically sensitive layer includes a second materialhaving a second bulk bandgap. The first optically sensitive layercomprises nanoparticles having a first diameter and the second opticallysensitive layer comprises nanoparticles having a second diameter. Atleast one of the optically sensitive layers comprises nanocrystalscomprising colloidal quantum dots. The quantum dots include a firstcarrier type and a second carrier type, wherein the first carrier typeis a flowing carrier and the second carrier type is one of asubstantially blocked carrier and a trapped carrier. The colloidalquantum dots include organic ligands, wherein a flow of at least one ofthe first carrier type and the second carrier type is related to theorganic ligands. At least one optically sensitive layers comprises acontinuous film of interconnected nanocrystal particles in contact withthe respective first electrode and the respective second electrode. Thenanocrystal particles comprise a plurality of nanocrystal cores and ashell over the plurality of nanocrystal cores. The plurality ofnanocrystal cores are fused. A physical proximity of the nanocrystalcores of adjacent nanocrystal particles provides electricalcommunication between the adjacent nanocrystal particles. The physicalproximity includes a separation distance of less than approximately 0.5nm. The electrical communication includes a hole mobility of at leastapproximately 1E-5 square centimeter per volt-second across thenanocrystal particles. The plurality of nanocrystal cores areelectrically interconnected with linker molecules. At least one of theoptically sensitive layers comprises a unipolar photoconductive layerincluding a first carrier type and a second carrier type, wherein afirst mobility of the first carrier type is higher than a secondmobility of the second carrier type. The persistence of each of theoptically sensitive layers is approximately equal. The persistence ofeach of the optically sensitive layers is approximately in a range of 1ms to 200 ms. The first optically sensitive layer comprises a firstmaterial having a first thickness, and the combination of the firstmaterial and the first thickness provides a first responsivity to lightof a first wavelength, wherein the second optically sensitive layercomprises a second material having a second thickness, and thecombination of the second material and the second thickness provides asecond responsivity to light of a second wavelength, wherein the firstresponsivity and the second responsivity are approximately equal. Thefirst responsivity and the second responsivity are approximately equal.

A photodetector of this embodiment has a first optically sensitive layercomprising a first material having a first thickness, and thecombination of the first material and the first thickness provides afirst photoconductive gain to light of a first wavelength, wherein thesecond optically sensitive layer comprises a second material having asecond thickness, and the combination of the second material and thesecond thickness provides a second photoconductive gain to light of asecond wavelength. The first photoconductive gain and the secondphotoconductive gain are approximately equal. The first opticallysensitive layer comprises a first material having a first thickness, andthe combination of the first material and the first thickness provides afirst absorbance to light of a first wavelength, wherein the secondoptically sensitive layer comprises a second material having a secondthickness, and the combination of the second material and the secondthickness provides a second absorbance to light of a second wavelength,wherein the first absorbance and the second absorbance are approximatelyequal. The first absorbance and the second absorbance are approximatelyequal. The second optically sensitive layer is relatively completelyabsorbent of light in a first wavelength interval and relativelycompletely transmissive of light outside the first wavelength interval.The first optically sensitive layer is relatively completely absorbentof the light outside the at least one first wavelength interval. Thefirst optically sensitive layer is relatively completely absorbent oflight in the first wavelength interval. The first optically sensitivelayer comprises a nanocrystal material having first photoconductive gainand the second optically sensitive layer comprises a nanocrystalmaterial having a second photoconductive gain. At least one of theoptically sensitive layers comprises a nanocrystal material havingphotoconductive gain and a responsivity of at least approximately 0.4amps/volt (A/V). The responsivity is achieved when a bias is appliedacross the at least one of the optically sensitive layers, wherein thebias is approximately in a range of 1 volt to 5 volts.

The photodetector of one embodiment has a first optically sensitivelayer comprises a nanocrystal material having first photoconductive gainand a first responsivity approximately in a range of 0.4 A/V to 100 A/V.The second optically sensitive layer comprises a nanocrystal materialhaving a second photoconductive gain and a second responsivityapproximately in a range of 0.4 A/V to 100 A/V. The secondphotoconductive gain is greater than the first photoconductive gain. Atleast one of the optically sensitive layers comprises nanocrystals of amaterial having a bulk bandgap, and wherein the nanocrystals are quantumconfined to have an effective bandgap more than twice the bulk bandgap.At least one of the optically sensitive layers includes nanocrystalscomprising nanoparticles, wherein a nanoparticle diameter of thenanoparticles is less than a Bohr exciton radius of bound electron-holepairs within the nanoparticle. 1, wherein a first diameter ofnanocrystals of the first optically sensitive layer is greater than asecond diameter of nanocrystals of the second optically sensitive layer.A first diameter of nanocrystals of the first optically sensitive layermay be less than a second diameter of nanocrystals of the secondoptically sensitive layer. At least one of the optically sensitivelayers comprises nanocrystals of a material having a bulk bandgap ofless than approximately 0.5 electron volts (eV), and wherein thenanocrystals are quantum confined to have a bandgap more than 1.0 eV.

In an embodiment, the photodetector has a first optically sensitivelayer comprises a first composition including one of lead sulfide (PbS),lead selenide (PbSe), lead tellurium sulfide (PbTe), indium phosphide(InP), indium arsenide (InAs), and germanium (Ge). In an embodiment, thephotodetector has a second optically sensitive layer comprises a secondcomposition including one of indium sulfide (In₂S₃), indium selenide(In₂Se₃), indium tellurium (In₂Te₃), bismuth sulfide (Bi₂S₃), bismuthselenide (Bi₂Se₃), bismuth tellurium (Bi₂Te₃), indium phosphide (InP),gallium arsenide (GaAs), silicon (Si), and germanium (Ge).

In an embodiment, each of the optically sensitive layers comprisesdifferent compound semiconductor nanocrystals, wherein the firstoptically sensitive layer comprises a composition including lead and thesecond optically sensitive layer comprises a composition including oneof indium and bismuth. Each of the optically sensitive layers comprisesnanocrystals of a material having a bulk bandgap of less thanapproximately 0.5 eV.

In an embodiment, the nanocrystals of at least one optically sensitivelayer are quantum confined to a bandgap corresponding to: 490 nmwavelength. or approximately 2.5 eV, or 560 nm wavelength orapproximately 2.2 eV, or approximately 1.8 eV, or 1.2 eV, orapproximately 0.9 eV, or approximately 0.7 eV, or corresponding to 630nm wavelength or corresponding to 650 nm wavelength. In an embodiment,the nanocrystals of at least one optically sensitive layer are quantumconfined to a bandgap corresponding to 670 nm wavelength. In anembodiment, the nanocrystals of at least one optically sensitive layerare quantum confined to a bandgap corresponding to 700 nm wavelength. Inan embodiment, the nanocrystals of at least one optically sensitivelayer are quantum confined to a bandgap corresponding to 800 nmwavelength. In an embodiment, the nanocrystals of at least one opticallysensitive layer are quantum confined to a bandgap corresponding to 900nm wavelength.

In an embodiment, the nanocrystals the nanocrystals of at least oneoptically sensitive layer are quantum confined to a bandgapcorresponding to 1000 nm wavelength. In an embodiment, the nanocrystalsof at least one optically sensitive layer are quantum confined to abandgap corresponding to 1300 nm wavelength. In an embodiment, thenanocrystals of at least one optically sensitive layer are quantumconfined to a bandgap corresponding to 1650 nm wavelength. In anembodiment, the nanocrystals of at least one optically sensitive layerare quantum confined to a bandgap corresponding to 3 um wavelength. Inan embodiment, the nanocrystals of at least one optically sensitivelayer are quantum confined to a bandgap corresponding to 5 umwavelength.

In an embodiment, this photodetector has an optical sensitivity of atleast one optically sensitive layer is at an intensity of light lessthan approximately 1 lux is more than twice the optical sensitivity ofthe optically sensitive material at an intensity of light of at least100 lux. In an embodiment, this photodetector has an optical sensitivityof at least one optically sensitive layer at an intensity of light lessthan approximately 1 lux is more than ten times the optical sensitivityof the optically sensitive material at an intensity of light of at least100 lux. In an embodiment, this photodetector has an optical sensitivityof at least one optically sensitive layer is more than 1000 mV/lux-s atrelatively low light levels and less than 500 mV/lux-s at relativelyhigh light levels. In an embodiment, this photodetector has an opticalsensitivity of at least one optically sensitive layer is more than 2000mV/lux-s at relatively low light levels and less than 400 mV/lux-s atrelatively high light levels. In an embodiment, this photodetector hasan optical sensitivity of at least one optically sensitive layer is morethan 3000 mV/lux-s at relatively low light levels and less than 300mV/lux-s at relatively high light levels.

In an embodiment, this photodetector has a sensitive layer comprising afirst absorption band including at least one first set of colors and isdevoid of a local absorption maximum. The second optically sensitivelayer comprises a second absorption band including at least one secondset of colors and is devoid of a local absorption maximum, wherein thesecond absorption band includes the first set of colors. The firstoptically sensitive layer comprises a nanocrystal material having anabsorption onset at a first wavelength and the second opticallysensitive layer comprises a nanocrystal material having an absorptiononset at a second wavelength, wherein the first wavelength is shorterthan the second wavelength, and a local absorption maximum is absentfrom an absorption spectrum of at least one of the first opticallysensitive layer and the second optically sensitive layer. Thephotodetector has a dark current of at least one optically sensitivelayer is different from a dark current of at least one other opticallysensitive layer. At least one optically sensitive layer is a nanocrystallayer having a dark current approximately in a range of 10 nanoamps (nA)per square centimeter (cm) to 500 nA per square cm. A compensationapplied to a signal from at least one optically sensitive layer isdifferent from a compensation applied to a signal from at least oneother optically sensitive layer.

In an embodiment, this photodetector comprises at least one black pixel,wherein a dark current compensation signal is received from a respectiveblack pixel and used to apply dark current correction to the signal. Thedark current compensation signal is separately and proportionallyapplied to signals of each optically sensitive layer. The dark currentcompensation signal corresponding to each respective optically sensitivelayer is received from a respective black pixel and applied to arespective signal of the respective optically sensitive layer.

In an embodiment, the photodetector has at least two optically sensitivelayers including a third optically sensitive layer, wherein the thirdoptically sensitive layer is over at least a portion of the secondoptically sensitive layer. The at least two optically sensitive layersinclude a fourth optically sensitive layer, wherein the fourth opticallysensitive layer is over at least a portion of the third opticallysensitive layer. The fourth optically sensitive layer comprises ananocrystal material absorptive to at least visible blue light andtransmissive to visible green light, visible red light, and infraredlight. The third optically sensitive layer comprises a nanocrystalmaterial absorptive to at least visible blue light and visible greenlight and transmissive to visible red light and infrared light. Thesecond optically sensitive layer comprises a nanocrystal materialabsorptive to at least visible blue light, visible green light, andvisible red light. The first optically sensitive layer comprises ananocrystal material absorptive to at least visible blue light, visiblegreen light, visible red light and infrared light. It further comprisesa fourth optically sensitive layer, the fourth optically sensitive layercomprising a doped silicon region on a substrate of the integratedcircuit, the fourth optically sensitive layer positioned below the firstoptically sensitive layer, the second optically sensitive layer, and thethird optically sensitive layer. In an embodiment, this photodetectorhas a fourth optically sensitive layer, the fourth optically sensitivelayer comprises a doped silicon region integrated with a substrate ofthe integrated circuit, the fourth optically sensitive layer positionedbelow the first optically sensitive layer, the second opticallysensitive layer, and the third optically sensitive layer. In anembodiment, a photodetector has a third optically sensitive layer, thethird optically sensitive layer comprising a doped silicon region on asubstrate of the integrated circuit, the third optically sensitive layerpositioned below the first optically sensitive layer and the secondoptically sensitive layer. The third optically sensitive layercomprising a doped silicon region integrated with a substrate of theintegrated circuit, the third optically sensitive layer positioned belowthe first optically sensitive layer and the second optically sensitivelayer.

Embodiments are directed to a photodetector comprising conversioncircuitry. An integrated circuit includes the conversion circuitry, theconversion circuitry located under the at least two optically sensitivelayers. The conversion circuitry is coupled to the integrated circuit.The conversion circuitry converts the signals from a first type to asecond type. The conversion circuitry converts the signal from an analogsignal to a digital signal. The conversion circuitry converts the signalfrom a digital signal to a analog signal.

Embodiments are directed to a photodetector comprising compensationcircuitry. The compensation circuitry is coupled to the integratedcircuit. An integrated circuit includes the compensation circuitry, thecompensation circuitry located under the at least two opticallysensitive layers. The compensation circuitry adjusts the signal tocompensate for different properties among the optically sensitivelayers. The compensation circuitry at least partially compensates fornonlinearity of the signal output from the optically sensitive layers.The compensation circuitry at least partially linearizes digital dataderived from the signal. The compensation circuitry at least partiallylinearizes the signal using a polynomial function. The compensationcircuitry at least partially linearizes the signal using piecewiselinear inversion of a relationship between intensity of the light andelectrical properties of at least one optically sensitive layer. Thecompensation circuitry at least partially compensates for variance in arate of current flow in at least one optically sensitive layer over anintegration period for a constant intensity of light. The compensationcircuitry at least partially compensates for variance in a rate ofcurrent flow in at least one optically sensitive layer over anintegration period for differing intensities of light. The compensationcircuitry at least partially compensates for variance in gain in atleast one optically sensitive layer over an integration period for aconstant intensity of light. The compensation circuitry at leastpartially compensates for variance in gain in at least one opticallysensitive layer over an integration period for differing intensities oflight. The compensation circuitry: at least partially compensates fornonlinearity of signals output from the optically sensitive layers; andat least partially compensates for a difference between dark currents ofsignals output from the optically sensitive layers.

In an embodiment, the compensation circuitry includes a read out circuitand demosaicing algorithm that outputs a corrected color matrix based onanalog quantities read out from the respective optically sensitivelayers. The corrected color matrix includes a red, green, blue (RGB)matrix. The compensation circuitry compensates for transmission leakagebetween layers of the optically sensitive layers. The compensationcircuitry includes image circuitry to generate image data. The firstoptically sensitive layer comprises a nanocrystal material having firstphotoconductive gain and the second optically sensitive layer comprisesa nanocrystal material having a second photoconductive gain, the imagecircuitry compensating for a difference between the firstphotoconductive gain and the second photoconductive gain. Thecompensation circuitry applies black level correction that compensatesfor a difference between dark currents among the at least two opticallysensitive layers by applying a plurality of dark current compensationsto the signal. The compensation circuitry applies a first dark currentcompensation to a first signal from the first optically sensitive layerand a second dark current compensation to a second signal from thesecond optically sensitive layer. The first dark current compensation isdifferent from the second dark current compensation.

In an embodiment, a photodetector comprises at least one black pixel.The at least one black pixel comprises at least two optically sensitiveopaque layers, a first optically sensitive opaque layer and a secondoptically sensitive opaque layer, the first optically sensitive opaquelayer and the second optically sensitive opaque layer each comprising anoptically sensitive layer covered with an opaque material, the firstoptically sensitive opaque layer over at least a portion of a blackpixel integrated circuit and the second optically sensitive opaque layerover the first optically sensitive opaque layer, wherein each opticallysensitive opaque layer is interposed between a respective firstelectrode of the black pixel and a respective second electrode of theblack pixel, wherein the integrated circuit selectively applies a biasto the respective first and second electrodes of the black pixel andreads a dark current signal from the optically sensitive opaque layers,wherein the dark current signal is related to the number of photonsreceived by the respective optically sensitive opaque layer. The blackpixel generates a dark current. The dark current density isapproximately in a range of 10 nanoamps (nA)/square centimeter (cm) to500 nA/square cm. The dark current compensations include subtracting thedark current from the signals of the optically sensitive layers indifferent proportions. The dark current compensations includesubtracting a first portion of the dark current from a first signal ofthe second optically sensitive layer and subtracting a second portion ofthe dark current from a second signal of the second optically sensitivelayer.

The photodetector of an embodiment has a first portion is larger thanthe second portion. The at least one black pixel comprises a first blackpixel corresponding to the first optically sensitive layer and a secondblack pixel corresponding to the second optically sensitive layer. Thefirst black pixel generates a first dark current and the second blackpixel that generates a second dark current. The dark currentcompensation includes subtracting the first dark current from a firstsignal of the first optically sensitive layer and subtracting the seconddark current from a second signal of the second optically sensitivelayer. The at least one black pixel comprises a plurality of blackpixels generating a plurality of dark currents, wherein the compensationcircuitry generates the plurality of dark current compensations from theplurality of dark currents. In an embodiment, the responsivities of eachof the optically sensitive layers are approximately equal when athickness of the second optically sensitive layer is less than athickness of the first optically sensitive layer. Also included isbandgap reference circuitry that has at least one of integrated in theintegrated circuit and coupled to the integrated circuit. The blacklevel correction is based on temperature monitoring by tracking avoltage from the bandgap reference circuitry. A fill factor of the pixelregion is at least 80 percent, wherein the fill factor is a ratio ofabsorbing area of each pixel region to a total area of the pixel region.The fill factor can also be approximately in a range of 80 percent to100 percent.

Embodiments are directed to a photodetector comprising: a plurality ofpixel regions, each pixel region having a respective first electrode anda respective second electrode; an optically sensitive material betweenthe first electrode and the second electrode, wherein the resultantdevice is non-rectifying; a transistor coupled to one of electrodes inelectrical communication with the optically-sensitive material, thetransistor including a gate configured to store charge, wherein therespective first electrode of a pixel region electrically communicateswith the gate, wherein charge stored at the gate is discharged by a flowof current through the optically sensitive material during anintegration period of time; and circuitry generating a signal from thegate based on the amount of charge remaining in the charge store afterthe integration period of time.

Embodiments are directed to a photodetector comprising: a pixel region,each pixel region having a first electrode and a second electrode; aplurality of layers of optically sensitive material disposed between thefirst electrode and the second electrode to create a non-rectifyingoptically sensitive device; a transistor coupled to the opticallysensitive material, the transistor including a gate configured to storecharge, wherein the respective first electrode of the pixel regionelectrically communicates with the gate, wherein charge stored at thegate is discharged by a flow of current through the optically sensitivematerial during an integration period of time; and circuitry generatinga signal from the gate based on the amount of charge remaining in thecharge store after the integration period of time.

Embodiments include a photodetector comprising: a pixel regioncomprising an optically sensitive material between a first electrode anda second electrode, wherein the non-rectifying optically sensitivedevice is non-rectifying; pixel circuitry electrically coupled to theoptically sensitive material, the pixel circuitry establishing a voltageover an integration period of time, wherein a signal is generated basedon the voltage after the integration period of time; a converterconfigured to convert the signal into digital pixel data. The pixelcircuitry comprises a charge store and integration circuitry toestablish the voltage based on intensity of light absorbed by theoptically sensitive material of the pixel region over the integrationperiod of time. The pixel circuitry includes at least one transistor inelectrical communication with the first electrode, wherein the chargestore comprises parasitic capacitance of the at least one transistor.The pixel circuitry includes a source follower transistor having a gatein electrical communication with the first electrode.

In an embodiment, the parasitic capacitance comprises a parasiticcapacitance between the gate and a source of the source followertransistor. The pixel circuitry includes a reset transistor having agate in electrical communication with the first electrode. The parasiticcapacitance comprises a parasitic capacitance between a source andstructures of a substrate of the reset transistor. The parasiticcapacitance comprises metal-to-metal parasitic capacitance between nodesof the pixel circuit. The parasitic capacitance comprisesmetal-to-substrate parasitic capacitance between the charge store nodeand a silicon substrate. The parasitic capacitance is approximately in arange of 0.5 to 3 Femto Farads. The parasitic capacitance isapproximately in a range of 1 to 2 Femto Farads.

Embodiments are directed to a method comprising: exposing an opticallysensitive material to light; generating a signal based on a current flowthrough the optically sensitive material; biasing the opticallysensitive material to operate as a current sink during a first period oftime; and biasing the optically sensitive material to operate as acurrent source during a second period of time. The first period of timeis an integration period during which a voltage is established based onthe current flow through the optically sensitive material. The secondperiod of time is a period of time during which a reset is applied tothe optically sensitive material, the reset including resetting avoltage difference across the optically sensitive material.

Embodiments include a method comprising: exposing an optically sensitivematerial to light; generating a signal based on a current flow throughthe optically sensitive material; applying at least one voltage to theoptically sensitive material; biasing the optically sensitive materialto operate as a current sink; biasing the optically sensitive materialto operate as a current source during a second period of time. Applyingat least one voltage comprises applying a first voltage to reset avoltage difference across the optically sensitive material. Applying atleast one voltage comprises establishing a second voltage, the secondvoltage biasing the optically sensitive material as the current sinkApplying at least one voltage comprises applying a third voltage totransfer a signal from the optically sensitive material for read out.

Embodiments are directed to a method comprising: providing a pluralityof pixel regions, each pixel region having a respective first electrodeand a common second electrode, wherein the common second electrode is acommon electrode for the plurality of pixel regions; reading out asignal from each of the pixel regions based on the intensity of lightabsorbed by the optically sensitive layer for the respective pixelregion during an integration period of time; and varying the voltage onthe common second electrode. The varying includes varying the voltage onthe common second electrode over the read out cycle.

Embodiments include a method comprising: providing a plurality of pixelregions, each pixel region having a respective first electrode and acommon second electrode, wherein the common second electrode is a commonelectrode for the plurality of pixel regions; reading out a signal fromeach of the pixel regions based on the intensity of light absorbed bythe optically sensitive layer for the respective pixel region during anintegration period of time; and controlling the voltage on the commonsecond electrode between a plurality of voltages.

Embodiments include a method comprising: providing a plurality of pixelregions, each pixel region having a respective first electrode and arespective second electrode; varying the voltage of the respective firstelectrode of each respective pixel region during an integration periodof time independently of the voltage of the respective first electrodeof other pixel regions in the plurality of pixel regions; reading out asignal from each of the pixel regions based on the intensity of lightabsorbed by the optically sensitive layer for the respective pixelregion during the integration period of time; and varying the voltage ofthe respective second electrode for all of the pixel regions. The methodfurther comprises simultaneously varying the voltage of the respectivesecond electrode for all of the pixel regions. The method furthercomprises varying the voltage of the respective second electrode for allof the pixel regions during a time period that is outside theintegration period of time. The respective second electrode is a commonsecond electrode, and the common second electrode is a common electrodefor the plurality of pixel regions. The respective second electrode ofeach pixel region is in electrical communication with the respectivesecond electrode of each other pixel region in the plurality of pixelregions. The respective second electrode of each pixel region ismaintained at substantially equivalent voltage as the respective secondelectrode of each other pixel region in the plurality of pixel regions.Varying the voltage of the respective first electrode and varying thevoltage of the respective second electrode comprises varying the voltagebetween at least two different voltages, a first voltage and a secondvoltage. Varying the voltage of the respective first electrode comprisesvarying the voltage of the respective first electrode between the firstvoltage and the second voltage during the integration period of time.Varying the voltage of the respective second electrode comprises varyingthe voltage of the respective second electrode between the first voltageand the second voltage outside the integration period of time. Thesecond voltage is provided to reset a voltage difference across theoptically sensitive material. The method further comprises biasing theoptically sensitive material to operate as a current sink. The methodfurther comprises biasing the optically sensitive material to operate asa current source. The method further comprises applying a transfervoltage to transfer a signal from the optically sensitive material forread out.

Embodiments are directed to an image sensor comprising: a plurality ofpixel regions, each pixel region including a respective first electrodeand a common second electrode, wherein the common second electrode is acommon electrode for the plurality of pixel regions; each pixel regioncomprising an optically sensitive material between the respective firstelectrode and the common second electrode; pixel circuitry for eachpixel region in electrical communication with the respective firstelectrode of the pixel region, the pixel circuitry for each pixel regionincluding integration circuitry to establish a voltage based on theintensity of light absorbed by the optically sensitive material of therespective pixel region over an integration period of time, the pixelcircuitry including read out circuitry to read out a signal after theintegration period of time; and bias circuitry in electricalcommunication with the common second electrode to vary the voltage ofthe common second electrode.

Embodiments are directed to an image sensor comprising: a plurality ofpixel regions, each pixel region including a respective first electrodeand a common second electrode, wherein the common second electrode is acommon electrode for the plurality of pixel regions; each pixel regioncomprising an optically sensitive material between the respective firstelectrode and the common second electrode; pixel circuitry for eachpixel region in electrical communication with the respective firstelectrode of the pixel region, the pixel circuitry for each pixel regionincluding integration circuitry configured to establish a voltage basedon current flow through the optically sensitive material during anintegration period of time, the pixel circuitry including read outcircuitry to read out a signal after the integration period of time; andbias circuitry in electrical communication with the common secondelectrode configured to vary the voltage of the common second electrode.

Embodiments are directed to an image sensor comprising: a plurality ofpixel regions, each pixel region including a respective first electrodeand a common second electrode; each pixel region comprising an opticallysensitive material between the respective first electrode and the commonsecond electrode; pixel circuitry for each pixel region in electricalcommunication with the respective first electrode of the pixel region,the pixel circuitry for each pixel region including integrationcircuitry to establish a voltage based on the intensity of lightabsorbed by the optically sensitive material of the respective pixelregion over an integration period of time; and bias circuitry configuredto vary the voltage of the respective second electrode of each pixelregion outside of the integration period of time.

Embodiments are directed to an image sensor comprising: a plurality ofpixel regions, each pixel region including a respective first electrodeand a common second electrode; each pixel region comprising an opticallysensitive material between the respective first electrode and the commonsecond electrode; pixel circuitry for each pixel region in electricalcommunication with the respective first electrode of the pixel region,the pixel circuitry for each pixel region including integrationcircuitry configured to establish a voltage based on current flowthrough the optically sensitive material during an integration period oftime; and bias circuitry configured to vary the voltage of therespective second electrode of each pixel region at the same time.

Embodiments are directed to an image sensor comprising: a plurality ofpixel regions, each pixel region including a respective first electrodeand a common second electrode; each pixel region comprising an opticallysensitive material between the respective first electrode and the commonsecond electrode; pixel circuitry for each pixel region in electricalcommunication with the respective first electrode of the pixel region,the pixel circuitry for each pixel region including integrationcircuitry configured to establish a voltage based on current flowthrough the optically sensitive material during an integration period oftime; and bias circuitry configured to vary the voltage of therespective second electrode of each pixel region outside of theintegration period of time.

Embodiments are directed to an image sensor comprising: a plurality ofpixel regions, each pixel region including a respective first electrodeand a common second electrode; each pixel region comprising an opticallysensitive material between the respective first electrode and the commonsecond electrode; pixel circuitry for each pixel region in electricalcommunication with the respective first electrode of the pixel region,the pixel circuitry for each pixel region including integrationcircuitry to establish a voltage based on the intensity of lightabsorbed by the optically sensitive material of the respective pixelregion over an integration period of time; and bias circuitry configuredto vary the voltage of the respective second electrode of each pixelregion at the same time. Read out circuitry is used to read out a signalafter the integration period of time. The respective second electrode ofeach pixel region is a common second electrode for each of the pixelregions. The respective second electrode of each pixel region is inelectrical communication with the respective second electrode of each ofthe other pixel regions in the plurality of pixel regions. The circuitryis configured to maintain the respective second electrode of each pixelregion at substantially the same voltage as the respective secondelectrode of each of the other pixel regions.

In an embodiment, the bias circuitry is configured to switch the voltageof the common electrode between a first voltage and a second voltage.The bias circuitry is configured to provide a first voltage during theintegration period of time and to provide a second voltage after theintegration period of time. The first voltage and the second voltagediffer by at least 0.5 volts. The first voltage and the second voltagediffer by at least 1 volt. The first voltage and the second voltagediffer by at least 1.5 volts. The first voltage and the second voltagediffer by at least 2 volts. The first voltage is selected to bias theoptically sensitive material as a current source and a second voltage isselected to bias the optically sensitive material as a current sink. Thebias circuitry is configured to switch the voltage of the commonelectrode between a first voltage, a second voltage and a third voltage.The first voltage, the second voltage and the third voltage can bedifferent from one another. The bias circuitry provides the firstvoltage to reset a voltage across the optically sensitive material priorto the integration period of time. The bias circuitry provides thesecond voltage second voltage during the integration period of time. Thebias circuitry provides the third voltage after the integration periodof time when the signal is read out. The bias circuitry provides thethird voltage to transfer the signal to the buffer circuitry andprovides the first voltage to reset the voltage difference prior to therow select circuitry selecting the respective row to read out the signalfrom the buffer.

In an embodiment, the pixel circuitry can comprise a diode. The firstvoltage is below a threshold voltage for current flow across the diodeand the second voltage is above a threshold voltage for current flowacross the diode. The pixel circuitry and optically sensitive materialcomprise a parasitic diode. The first voltage is below a thresholdvoltage for current flow across the parasitic diode and the secondvoltage is above a threshold voltage for current flow across theparasitic diode. The respective first electrode for each pixel region isindependent from the respective first electrodes for the other pixelregions. The pixel circuitry and bias circuitry repeat a cycle ofoperation in which a voltage difference is reset across the opticallysensitive material. The pixel circuit establishes a voltage based on thecurrent flow through the optically sensitive material during anintegration period and the signal is read out.

The embodiment includes row select circuitry to select a respective rowof pixel regions to be read out. It comprises a buffer to store a signalread out of the pixel circuitry. The pixel circuitry includes a read outtransistor, the read out transistor comprising a charge store and a gateof a source follower transistor in electrical communication with thefirst electrode. Each pixel region comprises vertically stacked pixelswith a common electrode that is common among vertical layers of thepixel region and common to other pixels, wherein a voltage of the commonelectrode is varied. The optically sensitive material hasphotoconductive gain when a voltage difference is applied across theoptically sensitive material and the optically sensitive layer isexposed to the light.

In an embodiment, the optically sensitive material comprisesmonodisperse nanocrystals. The optically sensitive material comprises acontinuous film of interconnected nanocrystal particles in contact withthe respective first electrode and the common electrode. The nanocrystalparticles comprise a plurality of nanocrystal cores and a shell over theplurality of nanocrystal cores. The plurality of nanocrystal cores arefused. A physical proximity of the nanocrystal cores of adjacentnanocrystal particles provides electrical communication between theadjacent nanocrystal particles. The physical proximity includes aseparation distance of less than approximately 0.5 nm. The electricalcommunication includes a hole mobility of at least approximately 1E-5square centimeter per volt-second across the nanocrystal particles. Theplurality of nanocrystal cores are electrically interconnected withlinker molecules. The optically sensitive material comprisesnanocrystals of a material having a bulk bandgap, and wherein thenanocrystals are quantum confined to have an effective bandgap more thantwice the bulk bandgap. The optically sensitive material includesnanocrystals comprising nanoparticles, wherein a nanoparticle diameterof the nanoparticles is less than a Bohr exciton radius of boundelectron-hole pairs within the nanoparticle.

In an embodiment, the image sensor has optically sensitive material thatcomprise nanocrystals of a material having a bulk bandgap of less thanapproximately 0.5 electron volts (eV), and wherein the nanocrystals arequantum confined to have a bandgap more than 1.0 eV. The opticallysensitive material comprises a unipolar photoconductive layer includinga first carrier type and a second carrier type, wherein a first mobilityof the first carrier type is higher than a second mobility of the secondcarrier type. The optically sensitive material is part of anon-rectifying optically sensitive device. A rate of the current flowthrough the optically sensitive material has a non-linear relationshipwith intensity of the light absorbed by the optically sensitivematerial. The gain of the optically sensitive material has a non-linearrelationship with intensity of the light absorbed by the opticallysensitive material.

In an embodiment, each pixel region comprises a vertically stackedpixel. The vertically stacked pixel comprises a plurality of opticallysensitive layers including a first optically sensitive layer and asecond optically sensitive layer interposed between the respective firstelectrode and the common second electrode, the first optically sensitivelayer overlying at least a portion of a first side of an integratedcircuit and the second optically sensitive layer overlying at least aportion of a second side of the first optically sensitive layer, theplurality of optically sensitive layers comprising the opticallysensitive material. It further comprises read out circuitry to read outa signal after the integration period of time, the signal includingpixel information corresponding to light absorbed by the opticallysensitive layers. A thickness of the second optically sensitive layer isdifferent than a thickness of the first optically sensitive layer. Athickness of the second optically sensitive layer is less than athickness of the first optically sensitive layer. The persistence ofeach of the optically sensitive layers is approximately equal, and maybe in a range of 1 ms to 200 ms. The second optically sensitive layer isrelatively completely absorbent of light in a first wavelength intervaland relatively completely transmissive of light outside the firstwavelength interval. The first optically sensitive layer is relativelycompletely absorbent of the light outside the first wavelength interval.The first wavelength interval corresponds to blue light. A first darkcurrent of the first optically sensitive layer is different than asecond dark current of the second optically sensitive layer.

In an embodiment, the first optically sensitive layer comprises a firstmaterial having a first thickness, and the combination of the firstmaterial and the first thickness provides a first responsivity to lightof a first wavelength, wherein the second optically sensitive layercomprises a second material having a second thickness, and thecombination of the second material and the second thickness provides asecond responsivity to light of a second wavelength, wherein the firstresponsivity and the second responsivity are approximately equal. Thefirst optically sensitive layer comprises a first material having afirst thickness, and the combination of the first material and the firstthickness provides a first photoconductive gain to light of a firstwavelength, wherein the second optically sensitive layer comprises asecond material having a second thickness, and the combination of thesecond material and the second thickness provides a secondphotoconductive gain to light of a second wavelength, wherein the firstphotoconductive gain and the second photoconductive gain areapproximately equal. The first optically sensitive layer comprises afirst material having a first thickness, and the combination of thefirst material and the first thickness provides a first absorbance tolight of a first wavelength, wherein the second optically sensitivelayer comprises a second material having a second thickness, and thecombination of the second material and the second thickness provides asecond absorbance to light of a second wavelength, wherein the firstabsorbance and the second absorbance are approximately equal. At leastone of the optically sensitive layers comprises nanocrystals of amaterial having a bulk bandgap, and wherein the nanocrystals are quantumconfined to have an effective bandgap more than twice the bulk bandgap.

In an embodiment, a first diameter of nanocrystals of the firstoptically sensitive layer is different than a second diameter ofnanocrystals of the second optically sensitive layer. The firstoptically sensitive layer may comprise a first composition including oneof lead sulfide (PbS), lead selenide (PbSe), lead tellurium sulfide(PbTe), indium phosphide (InP), indium arsenide (InAs), and germanium(Ge), and the second optically sensitive layer comprises a secondcomposition including one of indium sulfide (In₂S₃), indium selenide(In₂Se₃), indium tellurium (In₂Te₃), bismuth sulfide (Bi₂S₃), bismuthselenide (Bi₂Se₃), bismuth tellurium (Bi₂Te₃), indium phosphide (InP),silicon (Si), and germanium (Ge).

Embodiments are directed to an image sensor comprising: a plurality ofpixel regions, each pixel region including a respective first electrodeand a common second electrode; each pixel region comprising an opticallysensitive material between the respective first electrode and the commonsecond electrode; pixel circuitry for each pixel region in electricalcommunication with the respective first electrode of the pixel region,the pixel circuitry for each pixel region generating a signal based on acurrent flow through the optically sensitive material; and biascircuitry controlling a voltage of the respective second electrode ofeach pixel region to bias the optically sensitive material to operate asa current sink during a first period of time and to bias the opticallysensitive material to operate as a current source during a second periodof time. The bias circuitry varies the voltage of the respective secondelectrode of each pixel region nearly simultaneously.

In an embodiment, the pixel circuitry for each pixel region comprises acharge store and integration circuitry to establish a voltage based onthe intensity of light absorbed by the optically sensitive material ofthe respective pixel region over an integration period of time. Thepixel circuitry includes at least one transistor in electricalcommunication with the respective first electrode, wherein the chargestore comprises parasitic capacitance of the at least one transistor.The pixel circuitry includes a source follower transistor having a gatein electrical communication with the respective first electrode. Theparasitic capacitance comprises a parasitic capacitance between the gateand a source of the source follower transistor. The pixel circuitryincludes a reset transistor having a gate in electrical communicationwith the respective first electrode. The parasitic capacitance comprisesa parasitic capacitance between a source and structures of a substrateof the reset transistor. The parasitic capacitance comprisesmetal-to-metal parasitic capacitance between nodes of the pixel circuit.The parasitic capacitance comprises metal-to-substrate parasiticcapacitance between the charge store node and a silicon substrate. Theparasitic capacitance is approximately in a range of 0.5 to 3 FemtoFarads, or is approximately in a range of 1 to 2 Femto Farads. Theintegration circuitry establishes a voltage based on current flowthrough the optically sensitive material during the integration periodof time. The bias circuitry switches a voltage of the common electrodebetween a first voltage and a second voltage. The first voltage biasesthe optically sensitive material as a current source and the secondvoltage biases the optically sensitive material as a current sink. Thebias circuitry is configured to provide the first voltage during theintegration period of time and to provide the second voltage after theintegration period of time. The first voltage and the second voltagediffer by at least 0.5 volts, or by at least 1 volt, or by at least 1.5volts, or by at least 2 volts. The bias circuitry switches the voltageof the common electrode between a first voltage, a second voltage and athird voltage. The first voltage, the second voltage and the thirdvoltage can be different from one another. The bias circuitry providesthe first voltage to reset a voltage across the optically sensitivematerial prior to the integration period of time. The bias circuitryprovides the second voltage second voltage during the integration periodof time. The bias circuitry provides the third voltage after theintegration period of time when the signal is read out. The embodimentalso comprises read out circuitry to read out a signal after theintegration period of time

Embodiments are directed to an image sensor comprising: a semiconductorsubstrate; a plurality of pixel regions, each pixel region comprising anoptically sensitive layer over the substrate, the optically sensitivelayer positioned to receive light; a pixel circuit for each pixelregion, each pixel circuit comprising a charge store and a read outcircuit, the charge store and the read out circuit in electricalcommunication with the optically sensitive layer of the respective pixelregion; and conductive material positioned between the charge store ofthe respective pixel region and the optically sensitive layer of thecorresponding pixel region such that the respective charge store issubstantially shielded from the light incident on the opticallysensitive layer, wherein the light is in a wavelength band, wherein atleast a portion of the conductive material is a metal layer inelectrical communication with the optically sensitive layer. The pixelcircuit for each pixel region comprises a charge store and anintegration circuit to establish a voltage based on intensity of thelight absorbed by the optically sensitive material of the respectivepixel region over an integration period of time. The pixel circuitincludes at least one transistor in electrical communication with arespective first electrode of the respective pixel region, wherein thecharge store comprises parasitic capacitance of the at least onetransistor. The pixel circuit includes a source follower transistorhaving a gate in electrical communication with the respective firstelectrode. The parasitic capacitance comprises a parasitic capacitancebetween the gate and a source of the source follower transistor. Thepixel circuit includes a reset transistor having a gate in electricalcommunication with the respective first electrode. The parasiticcapacitance comprises a parasitic capacitance between a source andstructures of a substrate of the reset transistor. The parasiticcapacitance comprises metal-to-metal parasitic capacitance between nodesof the pixel circuit. The parasitic capacitance comprisesmetal-to-substrate parasitic capacitance between the charge store nodeand a silicon substrate. The parasitic capacitance is approximately in arange of 0.5 to 3 Femto Farads or approximately in a range of 1 to 2Femto Farads.

Embodiments include an image sensor comprising: a semiconductorsubstrate; a plurality of pixel regions, each pixel region comprising afirst electrode, a second electrode, and an optically sensitive layerover the substrate, the optically sensitive layer positioned to receivelight; a pixel circuit for each pixel region, each pixel circuitcomprising a charge store and a read out circuit, the charge store andthe read out circuit in electrical communication with the opticallysensitive layer of the respective pixel region; and conductive materialpositioned between the charge store of the respective pixel region andthe optically sensitive layer of the corresponding pixel region, theconductive material coupled to at least one electrode, the conductivematerial providing an opaque shield such that the respective chargestore is shielded from the light incident on the optically sensitivelayer when the light is in a wavelength band, wherein at least a portionof the conductive material is a metal layer in electrical communicationwith the optically sensitive layer.

Embodiments are directed to an image sensor comprising: a semiconductorsubstrate; a plurality of pixel regions, each pixel region comprising afirst electrode, a second electrode, and an optically sensitive layerover the substrate, the optically sensitive layer positioned to receivelight; a pixel circuit for each pixel region, each pixel circuitcomprising a charge store and a read out circuit, the charge store andthe read out circuit in electrical communication with the opticallysensitive layer of the respective pixel region; and a plurality ofconductive layers positioned between the charge store of the respectivepixel region and the optically sensitive layer of the correspondingpixel region, the conductive layers providing an opaque shield such thatthe respective charge store is shielded from the light incident on theoptically sensitive layer when the light is in a wavelength band,wherein a set of conductive layers of the plurality of conductive layersis in electrical communication with the optically sensitive layer. Theplurality of conductive layers includes at least three metal layers,wherein the set of conductive layers includes two metal layers of the atleast three metal layers. The second electrode is a common secondelectrode that is common to all pixel regions of the plurality of pixelregions, wherein the common second electrode is connected through aninterconnect metal layer, wherein the plurality of conductive layersincludes the interconnect metal layer. The charge store comprisescapacitance or parasitic capacitance, parasitic capacitance betweenmetal in an interconnect layer, or parasitic capacitance from a drain ofa reset transistor and gate of a read out transistor.

The image sensor may comprise a transistor coupled between the chargestore of each pixel circuit and the optically sensitive layer of thecorresponding pixel region, or a diode coupled between the charge storeof each pixel circuit and the optically sensitive layer of thecorresponding pixel region, or a parasitic diode coupled between thecharge store of each pixel circuit and the optically sensitive layer ofthe corresponding pixel region.

The image sensor of embodiments is configured such that each respectivepixel circuit resets a voltage difference across the optically sensitivelayer of the corresponding pixel region. Each respective pixel circuitindependently resets a voltage of the charge store of the respectivepixel circuit. Each respective pixel circuit comprises: a first resetcircuit in electrical communication with the charge store of therespective pixel circuit; a switch between the respective charge storeand a first electrode of the corresponding pixel region; and a secondreset circuit in electrical communication with the first electrode ofthe respective pixel region when the switch electrically isolates therespective first electrode from the charge store. A distance between thefirst electrode and the second electrode of each pixel region is lessthan approximately 3 micrometers, or 2 micrometers, or 1.5 micrometers.The optically sensitive layer for each pixel region has a top surfacearea of less than approximately 6 square micrometers, or 5 squaremicrometers, or 4 square micrometers.

In an embodiment, the pixel circuit applies a voltage difference acrossthe optically sensitive layer. The optically sensitive layer has aphotoconductive gain when the voltage difference is applied and theoptically sensitive layer is exposed to the light. The opticallysensitive layer comprises a nanocrystal material having photoconductivegain and a responsivity of at least approximately 0.4 amps/volt (A/V).The responsivity is achieved when a bias is applied across the opticallysensitive layer, wherein the bias is approximately in a range of 1 voltto 5 volts. The optically sensitive layer comprises monodispersenanocrystals. The optically sensitive layer comprises a continuous filmof interconnected nanocrystal particles in contact with the respectivefirst electrode and the common electrode. The nanocrystal particlescomprise a plurality of nanocrystal cores and a shell over the pluralityof nanocrystal cores. The plurality of nanocrystal cores are fused. Aphysical proximity of the nanocrystal cores of adjacent nanocrystalparticles provides electrical communication between the adjacentnanocrystal particles. The physical proximity includes a separationdistance of less than approximately 0.5 nm. The electrical communicationincludes a hole mobility of at least approximately 1E-5 squarecentimeter per volt-second across the nanocrystal particles. Theplurality of nanocrystal cores are electrically interconnected withlinker molecules. The optically sensitive layer comprises a unipolarphotoconductive layer including a first carrier type and a secondcarrier type, wherein a first mobility of the first carrier type ishigher than a second mobility of the second carrier type.

Embodiments are directed to a photodetector comprising: a semiconductorsubstrate; a plurality of pixel regions, each pixel region comprising anoptically sensitive layer over the substrate, the optically sensitivelayer positioned to receive light; and a pixel circuit for each pixelregion, each pixel circuit comprising a charge store and a switchingelement between the charge store and the optically sensitive layer forthe respective pixel region, the charge store and the switching elementone or more of integrated on and integrated in the semiconductorsubstrate below the plurality of pixel regions. The switching elementcontrols an integration period simultaneously for the plurality of pixelregions. Conductive material is positioned between the charge store ofthe respective pixel region and the optically sensitive layer of thecorresponding pixel region such that the respective charge store isshielded from the light incident on the optically sensitive layer,wherein the light is in a wavelength band, wherein at least a portion ofthe conductive material is a metal layer in electrical communicationwith the optically sensitive layer. The switching element is atransistor, or a diode, or a parasitic diode.

In an embodiment, the photodetector comprises an opaque material betweeneach pixel circuit and the corresponding pixel region, the opaquematerial shielding the charge store and the switching element from thelight received by the optically sensitive layer. It comprises circuitryconfigured to simultaneously switch the switching element of each of thepixel regions. Each pixel region comprises a respective first electrodeand a respective second electrode, wherein the optically sensitive layerof the respective pixel region is positioned between the respectivefirst electrode and the respective second electrode of the respectivepixel region. The pixel circuit transfers a voltage from the firstelectrode to the charge store when the switching element of therespective pixel region is in a first state and to block the transfer ofthe voltage from the first electrode to the charge store when theswitching element of the respective pixel region is in a second state.It comprises circuitry to switch the switching element of each of thepixel circuits from a first state to a second state at the same time foreach of the pixel circuits. It comprises circuitry to switch theswitching element of each of the pixel circuits after an integrationperiod of time.

In an embodiment, the photodetector comprises reset circuitry to reset avoltage difference across the optically sensitive layer while theswitching element is in the second state. It comprises reset circuitryto initiate another integration period of time while the switchingelement is in the second state. The reset circuitry comprising at leastone of a transistor, a diode, and a parasitic diode. The reset circuitryis configured to vary the voltage of the second electrode of each pixelregion to reset the voltage difference across the optically sensitivelayer. The reset circuitry resets the voltage difference across theoptically sensitive layer after the end of a respective integrationperiod and before all of the voltages transferred to the charge storefor the respective integration period have been selected to be read outby the read out circuitry. The reset circuitry initiates a nextsubsequent integration period before all of the voltages transferred tothe charge store for the prior integration period have been selected tobe read out by the read out circuitry. It has a reset circuit having afirst state to reset the voltage difference across the opticallysensitive layer, a second state to integrate charge based on the flow ofcurrent across the optically sensitive layer, and a third state totransfer a voltage from the first electrode to the charge store. It hasa first reset circuit to reset a voltage difference across the opticallysensitive layer after the end of a respective integration period and asecond reset circuit configured to reset the voltage of the chargestore. The first reset circuit resets the voltage difference while theswitching element is in the second state. The second reset circuitresets the charge store independently of the reset circuitry for thevoltage difference across the optically sensitive layer. It has read outcircuitry to read out a signal from the charge store for each pixelcircuit corresponding to a selected row of pixel regions.

The photodetector has a read out circuit is one or more of integrated onand integrated in the semiconductor substrate below the plurality ofpixel regions. The read out circuitry reads out sequential rows of thepixel regions. The optically sensitive layer of each pixel region ispositioned between a respective first electrode and a respective secondelectrode. A distance between the first electrode and the secondelectrode of each pixel region is less than approximately 3 micrometers,or less than approximately 2 micrometers, or less than approximately 1.5micrometers. In an embodiment, the optically sensitive layer for eachpixel region has a top surface area of less than approximately 6 squaremicrometers, or 5 square micrometers, or 4 square micrometers. The pixelcircuit applies a voltage difference across the optically sensitivelayer. The optically sensitive layer has a photoconductive gain when thevoltage difference is applied and the optically sensitive layer isexposed to the light. The optically sensitive layer comprises ananocrystal material having photoconductive gain and a responsivity ofat least approximately 0.4 amps/volt (A/V). The responsivity is achievedwhen a bias is applied across the optically sensitive layer, wherein thebias is approximately in a range of 1 volt to 5 volts.

In an embodiment of the photodetector, the optically sensitive layercomprises monodisperse nanocrystals. The optically sensitive layercomprises a continuous film of interconnected nanocrystal particles incontact with the respective first electrode and the common electrode.The nanocrystal particles comprise a plurality of nanocrystal cores anda shell over the plurality of nanocrystal cores. The plurality ofnanocrystal cores are fused. A physical proximity of the nanocrystalcores of adjacent nanocrystal particles provides electricalcommunication between the adjacent nanocrystal particles. The physicalproximity includes a separation distance of less than approximately 0.5nm. The electrical communication includes a hole mobility of at leastapproximately 1E-5 square centimeter per volt-second across thenanocrystal particles. The plurality of nanocrystal cores areelectrically interconnected with linker molecules. The opticallysensitive layer comprises a unipolar photoconductive layer including afirst carrier type and a second carrier type, wherein a first mobilityof the first carrier type is higher than a second mobility of the secondcarrier type.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a plurality of pixel regions over the semiconductorsubstrate, each pixel region comprising a respective first electrode, arespective second electrode and an optically sensitive layer between thefirst electrode and the second electrode; a pixel circuit for each pixelregion, each pixel circuit comprising a charge store, a switchingelement between the charge store and the optically sensitive layer forthe respective pixel region, and a read out circuit to sample a voltagefrom the charge store, the pixel circuit formed on the semiconductorsubstrate below the plurality of pixel regions; circuitry to switch theswitching element for all of the pixel circuits at substantially thesame time; wherein the distance between the respective first electrodeand the respective second electrode for each respective pixel region isless than approximately 2 micrometers, and a top surface area of eachpixel region is less than approximately 4 square micrometers; andwherein each pixel circuit is formed on a region of the semiconductorsubstrate below the plurality of pixel regions having an area less thanor equal to the top surface area of the corresponding pixel region. Ithas a via between each respective pixel circuit and the correspondingpixel region. Each pixel region has a corresponding pixel circuit withdedicated read out circuit, wherein the dedicated read out circuit isseparate from the read out circuit of the other pixel circuits. The areaof the semiconductor substrate for each respective pixel circuit ispositioned under a portion of the corresponding pixel region and aportion of an other pixel region that is not in electrical communicationthe respective pixel circuit.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a plurality of pixel regions over the substrate, each pixelregion comprising a respective first electrode, a respective secondelectrode and an optically sensitive layer between the first electrodeand the second electrode; a pixel circuit for each pixel region, eachpixel circuit comprising a charge store and a switching element betweenthe charge store and the first electrode for the respective pixelregion; global shutter circuitry to switch the switching element for allof the pixel circuits at substantially the same time; and bias circuitryconfigured to change the voltage of the second electrode for each of thepixel regions at substantially the same time. The plurality of pixelregions includes pixel regions for a plurality of rows and a pluralityof columns. Each pixel region includes a vertical stacked pixel, thevertical stacked pixel comprising at least two optically sensitivelayers, the two optically sensitive layers comprising the opticallysensitive layer and a second optically sensitive layer, the opticallysensitive layer over at least a portion of the semiconductor substrateand the second optically sensitive layer over the optically sensitivelayer. The global shutter circuitry switches the switching element forthe two optically sensitive layers for all of the pixel circuits atsubstantially the same time. The global shutter circuitry controls anintegration period simultaneously for the plurality of pixel regions. Ithas conductive material positioned between the charge store of therespective pixel region and the optically sensitive layer of thecorresponding pixel region such that the respective charge store isshielded from the light incident on the optically sensitive layer,wherein the light is in a wavelength band, wherein at least a portion ofthe conductive material is a metal layer in electrical communicationwith the optically sensitive layer.

In an embodiment, the switching element is a transistor, a diode, or aparasitic diode. An opaque material between each pixel circuit and thecorresponding pixel region, the opaque material shielding the chargestore and the switching element from the light received by the opticallysensitive layer. The pixel circuit transfers a voltage from the firstelectrode to the charge store when the switching element of therespective pixel region is in a first state and blocks the transfer ofthe voltage from the first electrode to the charge store when theswitching element of the respective pixel region is in a second state.The global shutter circuitry controls switching of the switching elementof each of the pixel circuits from a first state to a second state atthe same time for each of the pixel circuits. The global shuttercircuitry controls switching of the switching element of each of thepixel circuits after an integration period of time. It has resetcircuitry to reset a voltage difference across the optically sensitivelayer while the switching element is in the second state. It has resetcircuitry to initiate another integration period of time while theswitching element is in the second state. The reset circuitry comprisingat least one of a transistor, a diode, and a parasitic diode. The resetcircuitry is configured to vary the voltage of the second electrode ofeach pixel region to reset the voltage difference across the opticallysensitive layer. The reset circuitry resets the voltage differenceacross the optically sensitive layer after the end of a respectiveintegration period and before all of the voltages transferred to thecharge store for the respective integration period have been selected tobe read out by the read out circuitry. The reset circuitry initiates anext subsequent integration period before all of the voltagestransferred to the charge store for the prior integration period havebeen selected to be read out by the read out circuitry.

In one embodiment, a photodetector has a reset circuit having a firststate to reset the voltage difference across the optically sensitivelayer, a second state to integrate charge based on the flow of currentacross the optically sensitive layer, and a third state to transfer avoltage from the first electrode to the charge store. It has a firstreset circuit to reset a voltage difference across the opticallysensitive layer after the end of a respective integration period and asecond reset circuit configured to reset the voltage of the chargestore. The first reset circuit resets the voltage difference while theswitching element is in the second state. The second reset circuitresets the charge store independently of the reset circuitry for thevoltage difference across the optically sensitive layer.

In one embodiment, a photodetector comprises read out circuitry to readout a signal from the charge store for each pixel circuit correspondingto a selected row of pixel regions. The read out circuit is one or moreof integrated on and integrated in the semiconductor substrate below theplurality of pixel regions. The read out circuitry reads out sequentialrows of the pixel regions. A distance between the first electrode andthe second electrode of each pixel region is less than approximately 3micrometers, or 2 micrometers, or 1.5 micrometers.

In an embodiment, the optically sensitive layer for each pixel regionhas a top surface area of less than approximately 6 square micrometers.The optically sensitive layer for each pixel region has a top surfacearea of less than approximately 5 square micrometers. The opticallysensitive layer for each pixel region has a top surface area of lessthan approximately 4 square micrometers. The pixel circuit applies avoltage difference across the optically sensitive layer. The opticallysensitive layer has a photoconductive gain when the voltage differenceis applied and the optically sensitive layer is exposed to the light.The optically sensitive layer comprises a nanocrystal material havingphotoconductive gain and a responsivity of at least approximately 0.4amps/volt (A/V). The responsivity is achieved when a bias is appliedacross the optically sensitive layer, wherein the bias is approximatelyin a range of 1 volt to 5 volts. The optically sensitive layer comprisesmonodisperse nanocrystals. The optically sensitive layer comprises acontinuous film of interconnected nanocrystal particles in contact withthe respective first electrode and the common electrode. The nanocrystalparticles comprise a plurality of nanocrystal cores and a shell over theplurality of nanocrystal cores. The plurality of nanocrystal cores arefused. A physical proximity of the nanocrystal cores of adjacentnanocrystal particles provides electrical communication between theadjacent nanocrystal particles. The physical proximity includes aseparation distance of less than approximately 0.5 nm. The electricalcommunication includes a hole mobility of at least approximately 1E-5square centimeter per volt-second across the nanocrystal particles. Theplurality of nanocrystal cores are electrically interconnected withlinker molecules. The optically sensitive layer comprises a unipolarphotoconductive layer including a first carrier type and a secondcarrier type, wherein a first mobility of the first carrier type ishigher than a second mobility of the second carrier type.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a plurality of pixel regions over the substrate, each pixelregion comprising a plurality of optically sensitive layers over thesemiconductor substrate, each optically sensitive layer being positionedbetween a respective first electrode and a respective second electrode;a pixel circuit for each pixel region, each pixel circuit comprising acharge capture circuit for each optically sensitive layer of thecorresponding pixel region, the charge capture circuit comprising acharge store and a switching element between the charge store and thefirst electrode for the respective optically sensitive layer of thecorresponding pixel region; and global shutter circuitry to control theswitching element of the charge capture circuit for each opticallysensitive layer of each of the pixel regions at substantially the sametime. Each pixel circuit is formed on the semiconductor substrate belowthe plurality of pixel regions. Each pixel circuit applies a voltagedifference across the respective optically sensitive layer. Therespective optically sensitive layer has a photoconductive gain when thevoltage difference is applied and the optically sensitive layer isexposed to the light. The circuitry to control the switching element ofthe charge capture circuit for each optically sensitive layer of each ofthe pixel regions is global shutter circuitry. The global shuttercircuitry controls an integration period simultaneously for theplurality of pixel regions. Conductive material positioned between thecharge store of the respective pixel region and an optically sensitivelayer of a corresponding pixel region such that the respective chargestore is shielded from the light incident on the optically sensitivelayer, wherein the light is in a wavelength band, wherein at least aportion of the conductive material is a metal layer in electricalcommunication with the optically sensitive layer.

In an embodiment, the photodetector comprises an opaque material betweeneach pixel circuit and the corresponding pixel region, the opaquematerial shielding the charge store and the switching element from thelight received by the optically sensitive layer. The pixel circuittransfers a voltage from the respective first electrode to therespective charge store when the switching element is in a first stateand blocks the transfer of the voltage from the respective firstelectrode to the respective charge store when the switching element isin a second state. The global shutter circuitry controls switching ofthe switching element of each of the pixel circuits from a first stateto a second state at the same time for each of the pixel circuits. Theglobal shutter circuitry controls switching of the switching element ofeach of the pixel circuits after an integration period of time.

In one embodiment, a photodetector has reset circuitry to reset avoltage difference across each optically sensitive layer while theswitching element is in the second state. It has reset circuitry toinitiate another integration period of time while the switching elementis in the second state. It has reset circuitry comprising at least oneof a transistor, a diode, and a parasitic diode. The reset circuitryconfigured to vary the voltage of the respective second electrode ofeach corresponding pixel region to reset the voltage difference acrossthe corresponding optically sensitive layer. The reset circuitry resetsthe voltage difference across the corresponding optically sensitivelayer after the end of an integration period and before all of thevoltages transferred to the charge store for the respective integrationperiod have been selected to be read out by the read out circuitry. Thereset circuitry initiates a next subsequent integration period beforeall of the voltages transferred to the charge store for the priorintegration period have been selected to be read out by the read outcircuitry. The reset circuit has a first state to reset the voltagedifference across each optically sensitive layer, a second state tointegrate charge based on the flow of current across each opticallysensitive layer, and a third state to transfer a voltage from therespective first electrode to the respective charge store. It comprisesread out circuitry to read out a signal from the charge store for eachpixel circuit corresponding to a selected row of pixel regions. The readout circuit is one or more of integrated on and integrated in thesemiconductor substrate below the plurality of pixel regions. The readout circuitry reads out sequential rows of the pixel regions. A distancebetween the first electrode and the second electrode of each pixelregion is less than approximately 3 micrometers, or 2 micrometers, or1.5 micrometers.

In an embodiment, the optically sensitive layer for each pixel regionhas a top surface area of less than approximately 6, or 5, or 4 squaremicrometers. The pixel circuit applies a voltage difference across anoptically sensitive layer. At least one optically sensitive layer has aphotoconductive gain when the voltage difference is applied and theoptically sensitive layer is exposed to the light. At least oneoptically sensitive layer comprises a nanocrystal material havingphotoconductive gain and a responsivity of at least approximately 0.4amps/volt (A/V).

In an embodiment, responsivity is achieved when a bias is applied acrossthe optically sensitive layer, wherein the bias is approximately in arange of 1 volt to 5 volts. At least one optically sensitive layercomprises monodisperse nanocrystals. At least one optically sensitivelayer comprises a continuous film of interconnected nanocrystalparticles in contact with the respective first electrode and the commonelectrode. The nanocrystal particles comprise a plurality of nanocrystalcores and a shell over the plurality of nanocrystal cores. The pluralityof nanocrystal cores are fused. A physical proximity of the nanocrystalcores of adjacent nanocrystal particles provides electricalcommunication between the adjacent nanocrystal particles. The physicalproximity includes a separation distance of less than approximately 0.5nm. The electrical communication includes a hole mobility of at leastapproximately 1E-5 square centimeter per volt-second across thenanocrystal particles. The plurality of nanocrystal cores areelectrically interconnected with linker molecules. At least oneoptically sensitive layer comprises a unipolar photoconductive layerincluding a first carrier type and a second carrier type, wherein afirst mobility of the first carrier type is higher than a secondmobility of the second carrier type.

Embodiments are directed to an image sensor comprising: a semiconductorsubstrate; a plurality of pixel regions, each pixel region comprising anoptically sensitive layer over the semiconductor substrate, theoptically sensitive layer separated from the semiconductor substrate ona side by at least one adjacent layer, wherein vias couple the opticallysensitive layer and the semiconductor substrate; and a pixel circuit foreach pixel region, each pixel circuit comprising a charge store and aread out circuit, wherein the charge store is separate for each pixelregion and wherein the read out circuit is common with the read outcircuit for at least one set of other pixel regions.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a plurality of pixel regions, each pixel region comprising anoptically sensitive layer over the semiconductor substrate, theoptically sensitive layer creating a non-rectifying optically sensitivedevice, the optically sensitive layer separated from the semiconductorsubstrate on a side by at least one adjacent layer, wherein vias couplethe optically sensitive layer and the semiconductor substrate; and apixel circuit for each pixel region, each pixel circuit comprising acharge store and a read out circuit, wherein the charge store isseparate for each pixel region and wherein the read out circuit iscommon with the read out circuit for at least one set of other pixelregions.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a plurality of pixel regions, each pixel region comprising anoptically sensitive layer over the semiconductor substrate, theoptically sensitive layer creating a non-rectifying optically sensitivedevice, the optically sensitive layer separated from the semiconductorsubstrate on a side by at least one adjacent layer, wherein vias couplethe optically sensitive layer and the semiconductor substrate; a pixelcircuit for each pixel region, each pixel circuit establishing a voltageover an integration period of time, wherein the voltage has a non-linearrelationship with intensity of light absorbed by the optically sensitivelayer of the respective pixel region. The pixel circuit comprises acharge store and a read out circuit, wherein the charge store isseparate for each pixel region and wherein the read out circuit iscommon with the read out circuit for at least one set of other pixelregions.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a plurality of pixel regions, each pixel region comprising anoptically sensitive layer over the semiconductor substrate, theoptically sensitive layer separated from the semiconductor substrate ona side by at least one adjacent layer, wherein vias couple the opticallysensitive layer and the semiconductor substrate; and a pixel circuit foreach pixel region, each pixel circuit providing a current flow throughthe respective optically sensitive layer, wherein a rate of the currentflow through the respective optically sensitive layer has a non-linearrelationship with intensity of the light absorbed by the opticallysensitive layer. The pixel circuit comprises a charge store and a readout circuit, wherein the charge store is separate for each pixel regionand wherein the read out circuit is common with the read out circuit forat least one set of other pixel regions.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a plurality of pixel regions, each pixel region comprising anoptically sensitive layer over the semiconductor substrate, theoptically sensitive layer separated from the semiconductor substrate ona side by at least one adjacent layer, wherein vias couple the opticallysensitive layer and the semiconductor substrate; and a pixel circuit foreach pixel region, each pixel circuit providing a current flow throughthe respective optically sensitive layer, the current flow varying witha photoconductive gain of the optically sensitive layer, wherein thephotoconductive gain has a non-linear relationship with intensity of thelight absorbed by the optically sensitive layer. It has a charge storeand a read out circuit, wherein the charge store is separate for eachpixel region and wherein the read out circuit is common with the readout circuit for at least one set of other pixel regions.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a plurality of pixel regions, each pixel region comprising anoptically sensitive layer over the semiconductor substrate, theoptically sensitive layer comprising nanocrystals, the opticallysensitive layer separated from the semiconductor substrate on a side byat least one adjacent layer, wherein vias couple the optically sensitivelayer and the semiconductor substrate; and a pixel circuit for eachpixel region, each pixel circuit comprising a charge store and a readout circuit, wherein the charge store is separate for each pixel regionand wherein the read out circuit is common with the read out circuit forat least one set of other pixel regions.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a plurality of pixel regions, each pixel region comprising anoptically sensitive layer over the semiconductor substrate, theoptically sensitive layer separated from the semiconductor substrate ona side by at least one adjacent layer, wherein vias couple the opticallysensitive layer and the semiconductor substrate; and a pixel circuit foreach pixel region, each pixel circuit comprising a charge store and aread out circuit, wherein the charge store is separate for each pixelregion and wherein the read out circuit is common with the read outcircuit for at least one set of other pixel regions; wherein a darkcurrent of respective optically sensitive layers of respective pixelregions is different. The at least one adjacent layer comprises at leastone metal. The at least one adjacent layer comprises at least oneinsulator. The at least one adjacent layer comprises at least one of ametal layer and an insulator layer. The at least one set of other pixelregions includes three other pixel regions. The at least one set ofother pixel regions includes five other pixel regions. The at least oneset of other pixel regions includes seven other pixel regions. Eachpixel circuit is formed on the semiconductor substrate below theplurality of pixel regions.

In an embodiment each pixel circuit includes only a single transistorthat is not shared with an other pixel circuit. Each pixel circuitshares an amplifier and at least one transistor to transfer a voltagefrom the pixel circuit. Each pixel circuit shares a source followertransistor and at least one transistor to transfer a voltage from thepixel circuit.

In an embodiment, each pixel circuit shares a read out transistor and atleast one transistor to transfer a voltage from the pixel circuit.

In an embodiment, the pixel circuits corresponding to 16 pixel circuitscomprise less than 25 transistors. The pixel circuits comprise a singlenon-shared transistor for each of 16 pixel regions and two read outtransistors each shared by 8 pixel regions of the 16 pixel regions.

In an embodiment, the pixel circuits corresponding to 8 pixel circuitscomprise less than 16 transistors. The pixel circuits comprise a singlenon-shared transistor for each of 8 pixel regions, and at least one readout transistor shared by the 8 pixel regions.

In an embodiment, the pixel circuits corresponding to 8 pixel circuitscomprise at least two common transistors and each transistor has asingle separate transistor between the optically sensitive layer and theat least two common transistors.

In an embodiment, the two common transistors comprise a reset transistorand a row select transistor to transfer a voltage to a row buffer.

In an embodiment, the two common transistors comprise a source followertransistor.

In an embodiment, each pixel region includes a respective firstelectrode and a common second electrode, wherein the optically sensitivelayer adjoins the first electrode and the common second electrode,wherein the common second electrode is a common electrode for theplurality of pixel regions.

In an embodiment, the plurality of pixel regions including a verticalstacked pixel, the vertical stacked pixel comprising at least twooptically sensitive layers, a first optically sensitive layer and asecond optically sensitive layer, the first optically sensitive layerover at least a portion of the semiconductor substrate and the secondoptically sensitive layer over the first optically sensitive layer.

In an embodiment, a pixel circuit for each pixel region includes aplurality of sets of the pixel circuits for the at least two opticallysensitive layers.

In an embodiment, the plurality of sets of pixel circuits includes twosets of pixel circuits for two optically sensitive layers.

Embodiments include a photodetector comprising a semiconductorsubstrate; a plurality of pixel regions, each pixel region comprising anoptically sensitive layer over the substrate; a pixel circuit for eachpixel region, each pixel circuit comprising a charge store and a readout circuit; and circuitry to select the charge store of a plurality ofadjacent pixel regions for simultaneous reading to a shared read outcircuit. The plurality of adjacent pixel regions includes two adjacentpixel regions. The plurality of adjacent pixel regions includes fouradjacent pixel regions. The plurality of adjacent pixel regions includes16 adjacent pixel regions.

In an embodiment, the plurality of adjacent pixel regions is a number ofpixel regions, wherein the number is a multiple of two, or four, oreight, or sixteen.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a plurality of pixel regions over the semiconductorsubstrate, each pixel region comprising a first electrode, a secondelectrode and an optically sensitive layer between the first electrodeand the second electrode; a pixel circuit for each pixel region, eachpixel circuit comprising a charge store and a read out circuit;circuitry to electrically connect the first electrode for a set of pixelregions to a shared charge store during an integration period of time,the plurality of pixel regions including the set of pixel regions,wherein the shared charge store is the charge store corresponding to onepixel circuit of one pixel region; circuitry to read out a signal fromthe shared charge store, the signal based on intensity of light absorbedby each pixel region of the set of pixel regions during the integrationperiod of time. The set of pixel regions includes two pixel regions.

In an embodiment, the set of pixel regions includes four pixel regions,or 16 pixel regions.

In an embodiment, the set of pixel regions includes a number of pixelregions, wherein the number is a multiple of two or a multiple of four,or a multiple of eight, or a multiple of sixteen.

Embodiments include a photodetector comprising: a semiconductorsubstrate; a plurality of pixel regions over the semiconductorsubstrate, each pixel region comprising a first electrode, a secondelectrode and an optically sensitive layer between the first electrodeand the second electrode; pixel circuitry configured in a first mode toread out a signal for each pixel region based on the intensity of lightabsorbed by the optically sensitive layer of the respective pixelregion, and configured in a second mode to read out a signal for aplurality of sets of pixel regions based on the intensity of lightabsorbed by the optically sensitive layers of each set of pixel regions.The pixel circuitry electrically connects the first electrode of eachset of pixel regions to a common charge store for the respective set ofpixel regions for an integration period of time.

In an embodiment, the pixel circuitry is configured in the first mode toelectrically connect the first electrode of each pixel region to aseparate charge store for an integration period of time and isconfigured in the second mode to electrically connect the firstelectrodes for each set of pixel regions to a shared charge store forthe integration period of time.

In an embodiment, each set of pixel regions includes two pixel regionsor four pixel regions. In an embodiment, each set of pixel regionsincludes 16 pixel regions. Each set of pixel regions includes a numberof pixel regions, wherein the number is a multiple of two, or four, oreight, or sixteen.

Embodiments include a method comprising: providing a plurality of pixelregions, each pixel region comprising a first electrode, a secondelectrode and an optically sensitive layer between the first electrodeand the second electrode; electronically selecting a set of the pixelregions, wherein the plurality of pixel regions includes the set ofpixel regions; and reading out a signal from the set of the pixelregions, wherein the signal is based on intensity of light collectivelyabsorbed by the optically sensitive layers of the set of pixel regionsduring the integration period of time.

Embodiments include a method comprising: providing a plurality of pixelregions, each pixel region comprising a first electrode, a secondelectrode and an optically sensitive layer between the first electrodeand the second electrode; and selectively reading out a signal from aset of the pixel regions, the plurality of pixel regions including theset of pixel regions, the signal based on intensity of light absorbed bythe optically sensitive layers of the set of pixel regions during anintegration period of time.

Embodiments include a method comprising: providing a plurality of pixelregions, each pixel region comprising a first electrode, a secondelectrode and an optically sensitive layer between the first electrodeand the second electrode; providing a pixel circuit for each pixelregion, each pixel circuit comprising a charge store and a read outcircuit; selectively controlling connection of the first electrode for aset of pixel regions to a shared charge store during an integrationperiod of time, the plurality of pixel regions including the set ofpixel regions, wherein the shared charge store is a charge storecorresponding to one pixel circuit of one pixel region; and reading asignal from the shared charge store, the signal based on intensity oflight collectively absorbed by the set of pixel regions during theintegration period of time.

Embodiments include a method comprising: providing a plurality of pixelregions, each pixel region comprising a first electrode, a secondelectrode and an optically sensitive layer between the first electrodeand the second electrode; electronically selecting a set of the pixelregions, wherein the plurality of pixel regions includes the set ofpixel regions; reading out signals from the set of the pixel regions;and generating an image using the signals, wherein the signals are basedon intensity of light collectively absorbed by only the opticallysensitive layers of the set of pixel regions and represent less than allpixel data available from the plurality of pixel regions.

Embodiments include a method comprising: exposing a plurality of pixelregions to light, each pixel region comprising a first electrode, asecond electrode and an optically sensitive layer between the firstelectrode and the second electrode, wherein an intensity of the light isbelow a minimum threshold for signal generation in a first pixel regionof the pixel regions; providing a pixel circuit for each pixel region,each pixel circuit comprising a charge store and a read out circuit;selectively controlling connecting of the first electrode for a firstset of the pixel regions to a shared charge store during an integrationperiod of time, the first set of the pixel regions including the firstpixel region and at least one adjacent pixel region, wherein the sharedcharge store is a charge store corresponding to a pixel circuit of thefirst set of the pixel regions; and reading out a signal from the firstset of the pixel regions, wherein the signal is based on the intensityof light collectively absorbed by the optically sensitive layers of thefirst set of pixel regions during the integration period of time,wherein the intensity of the light collectively absorbed is above theminimum threshold.

Embodiments include a sensor comprising: at least one opticallysensitive layer; and a circuit comprising at least one node inelectrical communication with the optically sensitive layer, wherein thecircuit stores an electrical signal proportional to the intensity oflight incident on the optically sensitive layer during an integrationperiod, wherein a non-linear relationship exists between electricalcharacteristics of the optically sensitive layer and the intensity oflight absorbed by the optically sensitive layer, wherein a continuousfunction represents the non-linear relationship.

In an embodiment, at least one optically sensitive layer comprisesclosely-packed semiconductor nanoparticle cores.

In an embodiment, each core is partially covered with an incompleteshell, where the shell produces trap states having substantially asingle time constant.

In an embodiment, the nanoparticle cores comprise PbS partially coveredwith a shell comprising PbSO3.

In an embodiment, the nanoparticle cores are passivated using ligands ofat least two substantially different lengths.

In an embodiment, the nanoparticle cores are passivated using at leastone ligand of at least one length.

In an embodiment, the nanoparticle cores are passivated and crosslinkedusing at least one crosslinking molecule of at least one length.

In an embodiment, the crosslinking molecule is a conductive crosslinker.

In an embodiment, each nanoparticle core is covered with a shell, wherethe shell comprises PbSO3.

In an embodiment, the nanoparticle cores comprise PbS that is partiallyoxidized and substantially lacking in PbSO4 (lead sulfate).

In an embodiment, at least one optically sensitive layer comprises ananocrystalline solid, wherein at least a portion of a surface of thenanocrystalline solid is oxidized.

In an embodiment, a composition of the nanocrystalline solid excludes afirst set of native oxides and includes a second set of native oxides.

In an embodiment, the first set of native oxides includes PbSO4 (leadsulfate) and the second set of native oxides includes PbSO3.

In an embodiment, trap states of the nanocrystalline solid providepersistence, wherein an energy to escape from a predominant trap stateis less than or equal to approximately 0.1 eV.

In an embodiment, a non-predominant trap state, wherein an energy toescape from the non-predominant trap state is greater than or equal toapproximately 0.2 eV.

In an embodiment, a continuous transparent layer, the continuoustransparent layer comprising substantially transparent material, whereinthe continuous transparent layer at least partially covers the opticallysensitive layer.

In an embodiment, an adhesion layer anchoring constituents of theoptically sensitive layer to circuitry of the integrated circuit.

In an embodiment, the second optically sensitive layer comprises awavelength-selective light-absorbing material, wherein the firstoptically sensitive layer comprises a photoconductive material.

In an embodiment, an array of curved optical elements that determine adistribution of intensity across the optically sensitive layers.

In an embodiment, at least one optically sensitive layer comprisessubstantially fused nanocrystal cores having a dark current density lessthan approximately 0.1 nA/cm2.

In an embodiment, the circuit is an integrated circuit.

In an embodiment, a minimum feature spacing of the integrated circuit isin a range of approximately 100 nm to 200 um.

In an embodiment, the circuit is a complementary metal oxidesemiconductor (CMOS) integrated circuit.

In an embodiment, a rate of the current flow through the opticallysensitive layer has a non-linear relationship with the intensity oflight absorbed by the optically sensitive layer.

In an embodiment, a gain of the optically sensitive layer has anon-linear relationship with the intensity of light absorbed by theoptically sensitive layer.

In an embodiment, the optically sensitive layer has photoconductive gainwhen a voltage difference is applied across the optically sensitivelayer and the optically sensitive layer is exposed to light.

In an embodiment, persistence of the optically sensitive layer isapproximately in a range of 1 ms to 200 ms.

In an embodiment, the sensor is a non-rectifying device.

In an embodiment, the optically sensitive layer has a surface areadetermined by a width dimension and a length dimension.

In an embodiment, the width and/or length dimension is approximately 2um. In an embodiment, the width dimension and/or length is less thanapproximately 2 um.

In an embodiment, the optically sensitive layer comprises a continuousfilm of interconnected nanocrystal particles.

In an embodiment, the nanocrystal particles comprise a plurality ofnanocrystal cores and a shell over the plurality of nanocrystal cores.

In an embodiment, the plurality of nanocrystal cores are fused.

In an embodiment, a physical proximity of the nanocrystal cores ofadjacent nanocrystal particles provides electrical communication betweenthe adjacent nanocrystal particles.

In an embodiment, the physical proximity includes a separation distanceof less than approximately 0.5 nm.

In an embodiment, the electrical communication includes a hole mobilityof at least approximately 1E-5 square centimeter per volt-second acrossthe nanocrystal particles.

In an embodiment, the plurality of nanocrystal cores are electricallyinterconnected with linker molecules.

In an embodiment, the linker molecules include bidentate linkermolecules. The linker molecules can include ethanedithiol orbenzenedithiol.

In an embodiment, the optically sensitive layer comprises a unipolarphotoconductive layer including a first carrier type and a secondcarrier type, wherein a first mobility of the first carrier type ishigher than a second mobility of the second carrier type. The firstcarrier type is electrons or holes, and the second carrier type is holesor electrons.

In an embodiment, the optically sensitive layer comprises a nanocrystalmaterial having photoconductive gain and a responsivity of at leastapproximately 0.4 amps/volt (A/V).

In an embodiment, the responsivity is achieved under a biasapproximately in a range of 0.5 volts to 5 volts.

In an embodiment, the optically sensitive layer comprises nanocrystalsof a material having a bulk bandgap, and wherein the nanocrystals arequantum confined to have an effective bandgap more than twice the bulkbandgap.

In an embodiment, the optically sensitive layer includes nanocrystalscomprising nanoparticles, wherein a nanoparticle diameter of thenanoparticles is less than a Bohr exciton radius of bound electron-holepairs within the nanoparticle.

In an embodiment, the optically sensitive layer comprises monodispersenanocrystals.

In an embodiment, the optically sensitive layer comprises nanocrystals.

In an embodiment, the nanocrystals are colloidal quantum dots.

In an embodiment, the quantum dots include a first carrier type and asecond carrier type, wherein the first carrier type is a flowing carrierand the second carrier type is one of a substantially blocked carrierand a trapped carrier.

In an embodiment, the colloidal quantum dots include organic ligands,wherein a flow of at least one of the first carrier type and the secondcarrier type is related to the organic ligands.

In an embodiment, the optically sensitive layer can be biased as both acurrent sink and a current source.

In an embodiment, at least a first metal layer and a second metal layer,the optically sensitive layer in electrical communication with thesecond metal layer.

In an embodiment, the at least two metal layers include metalinterconnect layers.

In an embodiment, the second metal layer forms contacts in electricalcommunication with the optically sensitive layer.

In an embodiment, the contacts comprise an aluminum body, a firstcoating and a second coating, the first coating comprising titaniumnitride and positioned between the aluminum body and the opticallysensitive layer, the second coating comprising titanium oxynitride andpositioned between the first coating and the optically sensitive layer.

In an embodiment, the contacts comprise an aluminum body, a firstcoating and a second coating, the first coating comprising titaniumnitride and positioned between the aluminum body and the opticallysensitive layer, the second coating located between the first coatingand the optically sensitive layer and comprising a metal selected fromthe group consisting of gold, platinum, palladium, nickel and tungsten.

In an embodiment, the contacts are formed from a plurality of metalsub-layers, each metal sub-layer comprising a constituent selected fromthe group consisting of titanium nitride, titanium oxy nitride, gold,platinum, palladium, nickel and tungsten.

In an embodiment, the second metal layer consists of metal other thanaluminum, the metal including at least one layer selected from the groupconsisting of titanium nitride, titanium oxynitride, gold, platinum,palladium, nickel and tungsten.

In an embodiment, the second metal layer consists of metal other thancopper, the metal including at least one layer selected from the groupconsisting of titanium nitride, titanium oxynitride, gold, platinum,palladium, nickel and tungsten.

In an embodiment, the second metal layer comprises a constituentselected from the group consisting of titanium nitride, titaniumoxynitride, gold, platinum, palladium, nickel and tungsten.

In an embodiment, the optically sensitive layer makes direct contactwith the second metal layer.

In an embodiment, the optically sensitive layer comprises a coating onthe second metal layer.

In an embodiment, the metal layers comprise at least one additionalmetal layer between the first metal layer and the second metal layer.

In an embodiment, the first metal layer and the at least one additionalmetal layer comprises aluminum, wherein the at least one additionalmetal layer excludes aluminum.

In an embodiment, each of the first metal layer and the at least oneadditional metal layer comprises aluminum and titanium nitride, whereinthe at least one additional metal layer excludes aluminum.

In an embodiment, each of the first metal layer and the at least oneadditional metal layer excludes aluminum.

In an embodiment, each of the first metal layer and the at least oneadditional metal layer excludes copper.

In an embodiment, the first metal layer has a first thickness dimensionand the second metal layer has a second thickness dimension.

In an embodiment, the first metal layer has a first aspect ratio and thesecond metal layer has a second aspect ratio.

Embodiments include a sensor comprising: a first region of an opticallysensitive material; and a second region of the optically sensitivematerial, the second region covering at least a portion of the firstregion; wherein the optically sensitive material creates anon-rectifying optically sensitive device, wherein a non-linearrelationship exists between electrical characteristics of the opticallysensitive material and the intensity of light absorbed by the opticallysensitive material; wherein the first region and the second regionpossess substantially different spectral onset of absorption.

Embodiments include a sensor comprising: at least one opticallysensitive layer;

wherein a first region of the optically sensitive layer provideselectronic signals corresponding to an intensity of light incident onthe first region and lying within a first spectral region; wherein asecond region of the optically sensitive layer provides electronicsignals corresponding to the intensity of light incident on the secondregion and lying within a second spectral region. The first spectralregion includes at least one of a visible spectral region, an X-rayspectral region, an ultraviolet (UV) spectral region, a near infrared(IR) (NIR) spectral region, a short-wavelength IR (SWIR) spectralregion, and a mid-wavelength IR (MWIR) spectral region.

In an embodiment, the second spectral region includes at least one of avisible spectral region, an X-ray spectral region, an ultraviolet (UV)spectral region, a near infrared (IR) (NIR) spectral region, ashort-wavelength IR (SWIR) spectral region, and a mid-wavelength IR(MWIR) spectral region

Embodiments include photodetector comprising: an integrated circuit; andat least two optically sensitive layers, a first optically sensitivelayer and a second optically sensitive layer, the first opticallysensitive layer over at least a portion of the integrated circuit andthe second optically sensitive layer over the first optically sensitivelayer; wherein each optically sensitive layer is interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode; wherein the integrated circuit selectivelyapplies a bias to the electrodes and reads signals from the opticallysensitive layers, wherein the signal is related to the number of photonsreceived by the respective optically sensitive layer.

Embodiments include a vertically stacked pixel, comprising: a pluralityof optically sensitive layers including a first optically sensitivelayer and a second optically sensitive layer, the first opticallysensitive layer overlying at least a portion of a first side of anintegrated circuit and the second optically sensitive layer overlying atleast a portion of a second side of the first optically sensitive layer;a plurality of electrodes, wherein the plurality of optically sensitivelayers is interposed between a respective first electrode and arespective second electrode of the plurality of electrodes; and acoupling between the integrated circuit and the plurality of electrodesby which the integrated circuit selectively applies a bias and readsfrom the optically sensitive layers pixel information corresponding tolight absorbed by the optically sensitive layers.

Embodiments include a photodetector comprising: an integrated circuit;and at least two optically sensitive layers, a first optically sensitivelayer and a second optically sensitive layer, the first opticallysensitive layer over at least a portion of the integrated circuit andthe second optically sensitive layer over the first optically sensitivelayer; wherein each optically sensitive layer is interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode; wherein the integrated circuit selectivelyapplies a bias to the electrodes and reads signals from the opticallysensitive layers, wherein the signal is related to the number of photonsreceived by the respective optically sensitive layer; and wherein atleast one of the optically sensitive layers comprises nanocrystals of amaterial having a bulk bandgap, wherein the nanocrystals are quantumconfined to have an effective bandgap more than twice the bulk bandgap.

Embodiments include a photodetector comprising: an integrated circuit;and at least two optically sensitive layers, a first optically sensitivelayer and a second optically sensitive layer, the first opticallysensitive layer over at least a portion of the integrated circuit andthe second optically sensitive layer over the first optically sensitivelayer; wherein each optically sensitive layer is interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode; wherein the integrated circuit selectivelyapplies a bias to the electrodes and reads signals from the opticallysensitive layers, wherein the signal is related to the number of photonsreceived by the respective optically sensitive layer; and wherein eachof the at least two optically sensitive layers comprises nanocrystals ofdifferent materials and each of the different materials has a differentbulk bandgap.

Embodiments include a photodetector comprising: an integrated circuit;and at least two optically sensitive layers, a first optically sensitivelayer and a second optically sensitive layer, the first opticallysensitive layer over at least a portion of the integrated circuit andthe second optically sensitive layer over the first optically sensitivelayer; wherein each optically sensitive layer is interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode; wherein the integrated circuit selectivelyapplies a bias to the electrodes and reads signals from the opticallysensitive layers, wherein the signal is related to the number of photonsreceived by the respective optically sensitive layer; and wherein eachof the optically sensitive layers comprises nanocrystals having adifferent particle size.

Embodiments include a photodetector comprising: an integrated circuit;and at least two optically sensitive layers, a first optically sensitivelayer and a second optically sensitive layer, the first opticallysensitive layer over at least a portion of the integrated circuit andthe second optically sensitive layer over the first optically sensitivelayer; wherein each optically sensitive layer is interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode; wherein the integrated circuit selectivelyapplies a bias to the electrodes and reads signals from the opticallysensitive layers, wherein the signal is related to the number of photonsreceived by the respective optically sensitive layer; and wherein afirst increase in bandgap due to quantum confinement in the firstoptically sensitive layer is greater than a second increase in bandgapdue to quantum confinement in the second optically sensitive layer.

Embodiments include a photodetector comprising: an integrated circuit;and at least two optically sensitive layers, a first optically sensitivelayer and a second optically sensitive layer, the first opticallysensitive layer over at least a portion of the integrated circuit andthe second optically sensitive layer over the first optically sensitivelayer; wherein each optically sensitive layer is interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode; wherein the integrated circuit selectivelyapplies a bias to the electrodes and reads signals from the opticallysensitive layers, wherein the signal is related to the number of photonsreceived by the respective optically sensitive layer; and wherein athickness of at least one optically sensitive layer is different from athickness of at least one other optically sensitive layer.

Embodiments include a photodetector comprising: an integrated circuit;and at least two optically sensitive layers, a first optically sensitivelayer and a second optically sensitive layer, the first opticallysensitive layer over at least a portion of the integrated circuit andthe second optically sensitive layer over the first optically sensitivelayer; wherein each optically sensitive layer is interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode; wherein the integrated circuit selectivelyapplies a bias to the electrodes and reads signals from the opticallysensitive layers, wherein the signal is related to the number of photonsreceived by the respective optically sensitive layer; and wherein thefirst optically sensitive layer comprises a nanocrystal material havingfirst photoconductive gain and the second optically sensitive layercomprises a nanocrystal material having a second photoconductive gain.

Embodiments include a photodetector comprising: an integrated circuit;and at least two optically sensitive layers, a first optically sensitivelayer and a second optically sensitive layer, the first opticallysensitive layer over at least a portion of the integrated circuit andthe second optically sensitive layer over the first optically sensitivelayer; wherein each optically sensitive layer is interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode; wherein the integrated circuit selectivelyapplies a bias to the electrodes and reads signals from the opticallysensitive layers, wherein the signal is related to the number of photonsreceived by the respective optically sensitive layer; and wherein a darkcurrent of at least one optically sensitive layer is different from adark current of at least one other optically sensitive layer.

Embodiments are directed to a photodetector comprising: an integratedcircuit; and at least two optically sensitive layers, a first opticallysensitive layer and a second optically sensitive layer, the firstoptically sensitive layer over at least a portion of the integratedcircuit and the second optically sensitive layer over the firstoptically sensitive layer; wherein each optically sensitive layer isinterposed between two electrodes, the electrodes including a respectivefirst electrode and a respective second electrode; wherein theintegrated circuit selectively applies a bias to the electrodes andreads signals from the optically sensitive layers, wherein the signal isrelated to the number of photons received by the respective opticallysensitive layer; and wherein a compensation applied to a signal from atleast one optically sensitive layer is different from a compensationapplied to a signal from at least one other optically sensitive layer.

Embodiments include a photodetector comprising: an integrated circuit;and at least two optically sensitive layers, a first optically sensitivelayer and a second optically sensitive layer, the first opticallysensitive layer over at least a portion of the integrated circuit andthe second optically sensitive layer over the first optically sensitivelayer; wherein each optically sensitive layer is interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode; wherein the integrated circuit selectivelyapplies a bias to the electrodes and reads signals from the opticallysensitive layers, wherein the signal is related to the number of photonsreceived by the respective optically sensitive layer; and wherein a darkcurrent compensation signal is received from a black pixel andseparately and proportionally applied to signals of each opticallysensitive layer.

Embodiments include a photodetector comprising: an integrated circuit;and at least two optically sensitive layers, a first optically sensitivelayer and a second optically sensitive layer, the first opticallysensitive layer over at least a portion of the integrated circuit andthe second optically sensitive layer over the first optically sensitivelayer; wherein each optically sensitive layer is interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode; wherein the integrated circuit selectivelyapplies a bias to the electrodes and reads signals from the opticallysensitive layers, wherein the signal is related to the number of photonsreceived by the respective optically sensitive layer; and wherein a darkcurrent compensation signal corresponding to each respective opticallysensitive layer is received from a respective black pixel and applied toa respective signal of the respective optically sensitive layer.

Embodiments include a photodetector comprising: an integrated circuit;and at least two optically sensitive layers, a first optically sensitivelayer and a second optically sensitive layer, the first opticallysensitive layer over at least a portion of the integrated circuit andthe second optically sensitive layer over the first optically sensitivelayer; wherein each optically sensitive layer is interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode; wherein the integrated circuit selectivelyapplies a bias to the electrodes and reads signals from the opticallysensitive layers, wherein the signal is related to the number of photonsreceived by the respective optically sensitive layer; and wherein a darkcurrent of at least one optically sensitive layer is approximately in arange of 10 nanoamps (nA) per square centimeter (cm) to 500 nA persquare cm.

Embodiments include a photodetector comprising: at least two opticallysensitive layers, a first optically sensitive layer and a secondoptically sensitive layer, the first optically sensitive layer over atleast a portion of a substrate and the second optically sensitive layerover the first optically sensitive layer; wherein at least one opticallysensitive layer is a nanocrystal layer having a dark currentapproximately in a range of 10 nanoamps (nA) per square centimeter (cm)to 500 nA per square cm.

Embodiments are directed to a photodetector comprising: an integratedcircuit; and at least two optically sensitive layers, a first opticallysensitive layer and a second optically sensitive layer, the firstoptically sensitive layer over at least a portion of the integratedcircuit and the second optically sensitive layer over the firstoptically sensitive layer; wherein each optically sensitive layer isinterposed between two electrodes, the electrodes including a respectivefirst electrode and a respective second electrode; wherein theintegrated circuit selectively applies a bias to the electrodes andreads signals from the optically sensitive layers, wherein the signal isrelated to the number of photons received by the respective opticallysensitive layer; and wherein the first optically sensitive layercomprises a first composition including one of lead sulfide (PbS), leadselenide (PbSe), lead tellurium sulfide (PbTe), indium phosphide (InP),indium arsenide (InAs), and germanium (Ge), and the second opticallysensitive layer comprises a second composition including one of indiumsulfide (In₂S₃), indium selenide (In₂Se₃), indium tellurium (In₂Te₃),bismuth sulfide (Bi₂S₃), bismuth selenide (Bi₂Se₃), bismuth tellurium(Bi₂Te₃), indium phosphide (InP), silicon (Si), and germanium (Ge).

Embodiments include a photodetector comprising: an integrated circuit;and at least two optically sensitive layers, a first optically sensitivelayer and a second optically sensitive layer, the first opticallysensitive layer over at least a portion of the integrated circuit andthe second optically sensitive layer over the first optically sensitivelayer; wherein each optically sensitive layer is interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode; wherein the integrated circuit selectivelyapplies a bias to the electrodes and reads signals from the opticallysensitive layers, wherein the signal is related to the number of photonsreceived by the respective optically sensitive layer; and wherein thefirst optically sensitive layer comprises a nanocrystal material havingan absorption onset at a first wavelength and the second opticallysensitive layer comprises a nanocrystal material having an absorptiononset at a second wavelength, wherein the first wavelength is shorterthan the second wavelength, and a local absorption maximum is absentfrom an absorption spectrum of at least one of the first opticallysensitive layer and the second optically sensitive layer.

Embodiments include a photodetector comprising: at least two opticallysensitive layers, a first optically sensitive layer and a secondoptically sensitive layer, the first optically sensitive layer over atleast a portion of an integrated circuit and the second opticallysensitive layer over the first optically sensitive layer; wherein thefirst optically sensitive layer comprises a first absorption bandincluding at least one first set of colors and is devoid of a localabsorption maximum, and the second optically sensitive layer comprises asecond absorption band including at least one second set of colors andis devoid of a local absorption maximum, wherein the second absorptionband includes the first set of colors; wherein each optically sensitivelayer is interposed between a respective first electrode and arespective second electrode; and wherein the integrated circuitselectively applies a bias to the electrodes and reads signals from theoptically sensitive layers.

Embodiments include a photodetector comprising: an integrated circuit;and a plurality of optically sensitive layers including a firstoptically sensitive layer and a vertically stacked set of opticallysensitive layers, the first optically sensitive layer in at least aportion of the integrated circuit and the vertically stacked set ofoptically sensitive layers over the first optically sensitive layer;wherein the vertically stacked optically sensitive layer is interposedbetween a respective first electrode and a respective second electrode;wherein the integrated circuit selectively applies a bias to theelectrodes and reads signals from the vertically stacked opticallysensitive layers, wherein the signal is related to the number of photonsreceived by the respective vertically stacked optically sensitive layer.

Embodiments include a pixel array comprising a plurality ofphotodetectors, wherein each photodetector is a vertically stackedpixel, the vertically stacked pixel comprising: at least two opticallysensitive layers, a first optically sensitive layer and a secondoptically sensitive layer, the first optically sensitive layer over atleast a portion of the integrated circuit and the second opticallysensitive layer over the first optically sensitive layer; and aplurality of electrodes including at least two electrodes between whichthe two optically sensitive layers are interposed, the electrodesincluding a respective first electrode and a respective secondelectrode; a coupling between the integrated circuit and the pluralityof electrodes by which the integrated circuit selectively applies a biasand reads from the optically sensitive layers pixel informationcorresponding to light absorbed by the optically sensitive layers.

Embodiments are directed to a photosensor array comprising: anintegrated circuit; and a plurality of photodetectors over theintegrated circuit, wherein each photodetector forms a verticallystacked pixel that comprises, at least two optically sensitive layers, afirst optically sensitive layer and a second optically sensitive layer,the first optically sensitive layer over at least a portion of theintegrated circuit and the second optically sensitive layer over thefirst optically sensitive layer; and wherein each optically sensitivelayer is interposed between two electrodes, the electrodes including arespective first electrode and a respective second electrode, whereinthe integrated circuit is coupled to the electrodes and selectivelyapplies a bias to the electrodes and reads signals from the opticallysensitive layers, wherein the signals are related to the number ofphotons received by the respective optically sensitive layer.

In an embodiment, the signal represents light absorbed by at least oneoptically sensitive layer. The signal can be a voltage proportional tolight absorbed by at least one optically sensitive layer. The respectivefirst electrode and second electrode for the first optically sensitivelayer are different electrodes than the respective first electrode andsecond electrode for the second optically sensitive layer.

In an embodiment, the respective first electrode for the first opticallysensitive layer is a different electrode than the respective firstelectrode for the second optically sensitive layer.

In an embodiment, the second respective electrode for the secondoptically sensitive layer is a common electrode common to both the firstoptically sensitive layer and the second optically sensitive layer.

In an embodiment, each respective first electrode is in contact with therespective first optically sensitive layer.

In an embodiment, each respective second electrode is in contact withthe respective second optically sensitive layer.

In an embodiment, each respective first electrode is positionedlaterally relative to at least a portion of the respective secondelectrode.

In an embodiment, at least a portion of each respective second electrodeis on the same layer of the integrated circuit as the respective firstelectrode and the respective optically sensitive layer.

In an embodiment, the respective second electrode for the firstoptically sensitive layer and the second optically layer comprises acommon electrode.

In an embodiment, the common electrode extends vertically from the firstoptically sensitive layer to the second optically sensitive layer.

In an embodiment, the common electrode extends vertically from theintegrated circuit along a portion of the first optically sensitivelayer and the second optically sensitive layer.

In an embodiment, each respective second electrode is disposed aroundthe respective first electrode.

In an embodiment, the respective second electrode is configured toprovide a barrier to carriers around the first electrode.

In an embodiment, the respective second electrode for the firstoptically sensitive layer and the second optically sensitive layercomprises a common electrode disposed around the first electrode.

In an embodiment, the common electrode extends vertically from theintegrated circuit.

In an embodiment, the second electrode is at least partially transparentand is positioned over the respective optically sensitive layer.

In an embodiment, the respective first electrode and the respectivesecond electrode are non-transparent and separated by a distancecorresponding to a width dimension and a length dimension.

In an embodiment, the width and/or length dimension is approximately 2um.

In an embodiment, the width and/or length dimension is less thanapproximately 2 um.

In an embodiment, the respective second electrode for the firstoptically sensitive layer and the second electrode for the secondoptically sensitive layer is a common electrode for both the firstoptically sensitive layer and the second optically sensitive layer.

In an embodiment, the at least two optically sensitive layers includes athird optically sensitive layer, wherein the third optically sensitivelayer is over at least a portion of the second optically sensitivelayer, wherein the respective second electrode for the first opticallysensitive layer, the second electrode for the second optically sensitivelayer and the third electrode for the third layer is a common electrodefor the first optically sensitive layer, the second optically sensitivelayer and the third layer, wherein the common electrode isnon-transparent.

In an embodiment, a third optically sensitive layer integrated in theintegrated circuit, wherein the respective second electrode for thefirst optically sensitive layer and the second electrode for the secondoptically sensitive layer is a common electrode for both the firstoptically sensitive layer and the second optically sensitive layer,wherein the respective second electrode for the third layer is differentfrom the common electrode.

In an embodiment, at least one optically sensitive layer comprises acontinuous film of interconnected nanocrystal particles in contact withthe respective first electrode and the respective second electrode.

In an embodiment, the nanocrystal particles comprise a plurality ofnanocrystal cores and a shell over the plurality of nanocrystal cores.

In an embodiment, the plurality of nanocrystal cores are fused.

In an embodiment, a physical proximity of the nanocrystal cores ofadjacent nanocrystal particles provides electrical communication betweenthe adjacent nanocrystal particles.

In an embodiment, the physical proximity includes a separation distanceof less than approximately 0.5 nm.

In an embodiment, the electrical communication includes a hole mobilityof at least approximately 1E-5 square centimeter per volt-second acrossthe nanocrystal particles.

In an embodiment, the plurality of nanocrystal cores are electricallyinterconnected with linker molecules.

In an embodiment, the linker molecules include bidentate linkermolecules.

In an embodiment, the linker molecules include ethanedithiol, orbenzenedithiol.

In an embodiment, at least one of the optically sensitive layerscomprises a unipolar photoconductive layer including a first carriertype and a second carrier type, wherein a first mobility of the firstcarrier type is higher than a second mobility of the second carriertype.

In an embodiment, the respective second electrode for the firstoptically sensitive layer and the second optically layer comprises acommon electrode extending vertically from the first optically sensitivelayer to the second optically sensitive layer.

In an embodiment, a thickness of the second optically sensitive layer isdifferent than a thickness of the first optically sensitive layer.

In an embodiment, a thickness of the first optically sensitive layer isless than a thickness of the second optically sensitive layer.

In an embodiment, a thickness of the second optically sensitive layer isless than a thickness of the first optically sensitive layer.

In an embodiment, persistence of each of the optically sensitive layersis approximately equal.

In an embodiment, persistence of each of the optically sensitive layersis longer than approximately 1 millisecond (ms), or in a range of 1 msto 30 ms, or in a range of 1 ms to 100 ms, or in a range of 1 ms to 200ms, or in a range of 10 ms to 50 ms.

In an embodiment, at least one optically sensitive layer comprisesclosely-packed semiconductor nanoparticle cores. Each core is partiallycovered with an incomplete shell, where the shell produces trap stateshaving substantially a single time constant. The nanoparticle corescomprise PbS partially covered with a shell comprising PbSO3. Thenanoparticle cores are passivated using ligands of at least twosubstantially different lengths. The nanoparticle cores are passivatedusing at least one ligand of at least one length. The nanoparticle coresare passivated and crosslinked using at least one crosslinking moleculeof at least one length. The crosslinking molecule is a conductivecrosslinker. Each nanoparticle core is covered with a shell, where theshell comprises PbSO3. The nanoparticle cores comprise PbS that ispartially oxidized and substantially lacking in PbSO4 (lead sulfate).

In an embodiment, at least one optically sensitive layer comprises ananocrystalline solid, wherein at least a portion of a surface of thenanocrystalline solid is oxidized.

In an embodiment, a composition of the nanocrystalline solid excludes afirst set of native oxides and includes a second set of native oxides.

In an embodiment, the first set of native oxides includes PbSO4 (leadsulfate) and the second set of native oxides includes PbSO3.

In an embodiment, trap states of the nanocrystalline solid providepersistence, wherein an energy to escape from a predominant trap stateis less than or equal to approximately 0.1 eV.

In an embodiment, a non-predominant trap state, wherein an energy toescape from the non-predominant trap state is greater than or equal toapproximately 0.2 eV.

In an embodiment, a continuous transparent layer, the continuoustransparent layer comprising substantially transparent material, whereinthe continuous transparent layer at least partially covers the opticallysensitive layer.

In an embodiment, an adhesion layer anchoring constituents of theoptically sensitive layer to circuitry of the integrated circuit.

In an embodiment, the second optically sensitive layer comprises awavelength-selective light-absorbing material, wherein the firstoptically sensitive layer comprises a photoconductive material.

In an embodiment, an array of curved optical elements that determine adistribution of intensity across the optically sensitive layers.

In an embodiment, at least one optically sensitive layer comprisessubstantially fused nanocrystal cores having a dark current density lessthan approximately 0.1 nA/cm2.

In an embodiment, a thickness of the second optically sensitive layer isless than a thickness of the first optically sensitive layer.

In an embodiment, the second optically sensitive layer is relativelycompletely absorbent of light in a first wavelength interval andrelatively completely transmissive of light outside the first wavelengthinterval.

In an embodiment, the first optically sensitive layer is relativelycompletely absorbent of the light outside the first wavelength interval.The first wavelength interval corresponds to blue light. A second darkcurrent of the second optically sensitive layer is less than a firstdark current of the first optically sensitive layer.

In an embodiment, responsivities of each of the optically sensitivelayers are approximately equal.

In an embodiment, the first optically sensitive layer comprises a firstmaterial having a first thickness, and the combination of the firstmaterial and the first thickness provides a first responsivity to lightof a first wavelength, wherein the second optically sensitive layercomprises a second material having a second thickness, and thecombination of the second material and the second thickness provides asecond responsivity to light of a second wavelength, wherein the firstresponsivity and the second responsivity are approximately equal.

In an embodiment, the first optically sensitive layer comprises a firstmaterial having a first thickness, and the combination of the firstmaterial and the first thickness provides a first photoconductive gainto light of a first wavelength, wherein the second optically sensitivelayer comprises a second material having a second thickness, and thecombination of the second material and the second thickness provides asecond photoconductive gain to light of a second wavelength, wherein thefirst photoconductive gain and the second photoconductive gain areapproximately equal.

In an embodiment, the first optically sensitive layer comprises a firstmaterial having a first thickness, and the combination of the firstmaterial and the first thickness provides a first absorbance to light ofa first wavelength, wherein the second optically sensitive layercomprises a second material having a second thickness, and thecombination of the second material and the second thickness provides asecond absorbance to light of a second wavelength, wherein the firstabsorbance and the second absorbance are approximately equal.

In an embodiment, gains of each of the optically sensitive layers areapproximately equal. The persistence of each of the optically sensitivelayers is approximately equal.

In an embodiment, a thickness of the first optically sensitive layer isless than a thickness of the second optically sensitive layer.

In an embodiment, the at least two optically sensitive layers includes athird optically sensitive layer, wherein the third optically sensitivelayer is over at least a portion of the second optically sensitive,wherein a thickness of the third optically sensitive layer is less thana thickness of the first optically sensitive layer and the secondoptically sensitive layer.

In an embodiment, a thickness of the third optically sensitive layer isless than a thickness of the first optically sensitive layer and thesecond optically sensitive layer.

In an embodiment, a thickness of the second optically sensitive layer isless than a thickness of the first optically sensitive layer.

In an embodiment, the third optically sensitive layer is relativelycompletely absorbent of light in a first wavelength interval andrelatively completely transmissive of light outside the first wavelengthinterval

In an embodiment, the second optically sensitive layer is relativelycompletely absorbent of light in a second wavelength interval andrelatively completely transmissive of light outside the secondwavelength interval, wherein the second wavelength interval includes andis larger than the first wavelength interval.

In an embodiment, the first optically sensitive layer is relativelycompletely absorbent of light in a third wavelength interval, whereinthe third wavelength interval includes and is larger than the secondwavelength interval.

In an embodiment, a third dark current of the third optically sensitivelayer is less than a second dark current of the second opticallysensitive layer.

In an embodiment, a third dark current of the third optically sensitivelayer is less than a first dark current of the first optically sensitivelayer.

In an embodiment, a second dark current of the second opticallysensitive layer is less than a first dark current of the first opticallysensitive layer.

In an embodiment, at least two optically sensitive layers includes afourth optically sensitive layer, wherein the fourth optically sensitivelayer is over at least a portion of the third optically sensitive layer,wherein a thickness of the fourth optically sensitive layer is less thana thickness of one of the first optically sensitive layer, the secondoptically sensitive layer, and the third optically sensitive layer.

In an embodiment, a thickness of the fourth optically sensitive layer isless than a thickness of the third optically sensitive layer.

In an embodiment, a thickness of the third optically sensitive layer isless than a thickness of the second optically sensitive layer.

In an embodiment, a thickness of the second optically sensitive layer isless than a thickness of the first optically sensitive layer.

In an embodiment, the fourth optically sensitive layer is relativelycompletely absorbent of light in a first wavelength interval andrelatively completely transmissive of light outside the first wavelengthinterval

In an embodiment, the third optically sensitive layer is relativelycompletely absorbent of light in a third wavelength interval andrelatively completely transmissive of light outside the third wavelengthinterval, wherein the third wavelength interval includes and is largerthan the fourth wavelength interval.

In an embodiment, the second optically sensitive layer is relativelycompletely absorbent of light in a second wavelength interval, whereinthe second wavelength interval includes and is larger than the thirdwavelength interval.

In an embodiment, the first optically sensitive layer is relativelycompletely absorbent of light in a first wavelength interval, whereinthe first wavelength interval includes and is larger than the secondwavelength interval.

In an embodiment, a fourth dark current of the fourth opticallysensitive layer is less than at least one of a third dark current of thethird optically sensitive layer, a second dark current of the secondoptically sensitive layer, and a first dark current of the firstoptically sensitive layer.

In an embodiment, a third dark current of the third optically sensitivelayer is less than at least one of a fourth dark current of the fourthoptically sensitive layer, a second dark current of the second opticallysensitive layer, and a first dark current of the first opticallysensitive layer.

In an embodiment, a second dark current of the second opticallysensitive layer is less than at least one of a fourth dark current ofthe fourth optically sensitive layer, a third dark current of the thirdoptically sensitive layer, and a first dark current of the firstoptically sensitive layer.

In an embodiment, a first dark current of the first optically sensitivelayer is less than at least one of a fourth dark current of the fourthoptically sensitive layer, a third dark current of the third opticallysensitive layer, and a second dark current of the second opticallysensitive layer.

In an embodiment, at least one of the optically sensitive layerscomprises a unipolar photoconductive layer including a first carriertype and a second carrier type, wherein a first mobility of the firstcarrier type is higher than a second mobility of the second carriertype.

In an embodiment, the first carrier type is electrons and the secondcarrier type is holes.

In an embodiment, the first carrier type is holes and the second carriertype is electrons.

In an embodiment, each of the optically sensitive layers comprises aunipolar photoconductive layer including a first carrier type and asecond carrier type, wherein a first mobility of the first carrier typeis higher than a second mobility of the second carrier type.

In an embodiment, the first carrier type is electrons and the secondcarrier type is holes.

In an embodiment, the first carrier type is holes and the second carriertype is electrons.

In an embodiment, the first optically sensitive layer comprises ananocrystal material having first photoconductive gain and the secondoptically sensitive layer comprises a nanocrystal material having asecond photoconductive gain.

In an embodiment, at least one of the optically sensitive layerscomprises a nanocrystal material having photoconductive gain and aresponsivity of at least approximately 0.4 amps/volt (A/V).

In an embodiment, the responsivity is achieved when a bias is appliedbetween the respective first electrode and the respective secondelectrode, wherein the bias is approximately in a range of 1 volt to 5volts. In an embodiment, the bias is approximately 0.5 volts, 1 volt,1.2 volts, or 1.5 volts.

In an embodiment, the first optically sensitive layer comprises ananocrystal material having first photoconductive gain and a firstresponsivity approximately in a range of 0.4 A/V to 100 A/V.

In an embodiment, the second optically sensitive layer comprises ananocrystal material having a second photoconductive gain and a secondresponsivity approximately in a range of 0.4 A/V to 100 A/V.

In an embodiment, the second photoconductive gain is greater than thefirst photoconductive gain.

In an embodiment, at least one of the optically sensitive layerscomprises nanocrystals of a material having a bulk bandgap, and whereinthe nanocrystals are quantum confined to have an effective bandgap morethan twice the bulk bandgap.

In an embodiment, at least one of the optically sensitive layersincludes nanocrystals comprising nanoparticles, wherein a nanoparticlediameter of the nanoparticles is less than a Bohr exciton radius ofbound electron-hole pairs within the nanoparticle.

In an embodiment, a first diameter of nanocrystals of the firstoptically sensitive layer is greater than a second diameter ofnanocrystals of the second optically sensitive layer.

In an embodiment, a first diameter of nanocrystals of the firstoptically sensitive layer is less than a second diameter of nanocrystalsof the second optically sensitive layer.

In an embodiment, at least one of the optically sensitive layerscomprises nanocrystals of a material having a bulk bandgap of less thanapproximately 0.5 electron volts (eV), and wherein the nanocrystals arequantum confined to have a bandgap more than 1.0 eV.

In an embodiment, at least one of the optically sensitive layerscomprises nanocrystals quantum confined to a bandgap corresponding to490 nm wavelength and approximately 2.5 eV.

In an embodiment, at least one of the optically sensitive layerscomprises nanocrystals quantum confined to a bandgap corresponding to560 nm wavelength and approximately 2.2 eV.

In an embodiment, at least one of the optically sensitive layerscomprises nanocrystals quantum confined to a bandgap corresponding to700 nm wavelength and approximately 1.8 eV.

In an embodiment, at least one of the optically sensitive layerscomprises nanocrystals quantum confined to a bandgap corresponding to1000 nm wavelength and approximately 1.2 eV.

In an embodiment, at least one of the optically sensitive layerscomprises nanocrystals quantum confined to a bandgap corresponding to1400 nm wavelength and approximately 0.9 eV.

In an embodiment, at least one of the optically sensitive layerscomprises nanocrystals quantum confined to a bandgap corresponding to1700 nm wavelength and approximately 0.7 eV.

In an embodiment, at least one of the optically sensitive layerscomprises nanocrystals of a material having a bulk bandgap approximatelyin a spectral range of 700 nanometer (nm) wavelength to 10 micrometer(um) wavelength, and wherein the nanocrystals are quantum confined tohave a bandgap approximately in a spectral range of 400 nm to 700 nm.

In an embodiment, at least one of the optically sensitive layerscomprises quantum confined nanocrystals having a diameter of less thanapproximately 1.5 nm.

In an embodiment, each of the optically sensitive layers comprisesnanocrystals of a material having a bulk bandgap of less than 0.5 eV,and wherein the nanocrystals in the first optically sensitive layer arequantum confined to have a bandgap of approximately 2.2 eV and thenanocrystals in the second optically sensitive layer are quantumconfined to have a bandgap of more than approximately 2.5 eV.

In an embodiment, each of the optically sensitive layers comprisesnanocrystals of a material having a bulk bandgap of less thanapproximately 0.5 eV.

In an embodiment, the nanocrystals of the second optically sensitivelayer are quantum confined to a bandgap corresponding to 490 nmwavelength.

In an embodiment, the nanocrystals of the second optically sensitivelayer are quantum confined to a bandgap of approximately 2.5 eV.

In an embodiment, the nanocrystals of the first optically sensitivelayer are quantum confined to a bandgap corresponding to 560 nmwavelength.

In an embodiment, the nanocrystals of the first optically sensitivelayer are quantum confined to a bandgap of approximately 2.2 eV.

In an embodiment, a photoconductive component in the integrated circuit,wherein the photoconductive component is optically sensitive in aspectral range of 700 nm to 10 um wavelength.

In an embodiment, the at least two optically sensitive layers include athird optically sensitive layer.

In an embodiment, the third optically sensitive layer is on theintegrated circuit.

In an embodiment, the third optically sensitive layer is integrated withthe integrated circuit.

In an embodiment, each of the optically sensitive layers comprisesnanocrystals of a material having a bulk bandgap of less than 0.5 eV.

In an embodiment, the nanocrystals in the first optically sensitivelayer are quantum confined to have a bandgap of approximately 2.2 eV andthe nanocrystals in the second optically sensitive layer are quantumconfined to have a bandgap of more than approximately 2.5 eV.

In an embodiment, the third optically sensitive layer senses lightapproximately in a spectral range of 700 nm to 10 um wavelength and thenanocrystals in the third optically sensitive layer are quantum confinedto have a bandgap of more than approximately 1.8 eV.

In an embodiment, the third optically sensitive layer is a siliconphotodiode.

In an embodiment, the at least two optically sensitive layers includes athird optically sensitive layer, wherein the third optically sensitivelayer is over at least a portion of the second optically sensitivelayer.

In an embodiment, each of the optically sensitive layers comprisesnanocrystals of a material having a bulk bandgap of less than 0.5 eV,and wherein the nanocrystals in the first optically sensitive layer arequantum confined to have a bandgap of approximately 1.8 eV, thenanocrystals in the second optically sensitive layer are quantumconfined to have a bandgap of approximately 2.2 eV, and the nanocrystalsin the third optically sensitive layer are quantum confined to have abandgap of more than approximately 2.5 eV.

In an embodiment, each of the optically sensitive layers comprisesnanocrystals of a material having a bulk bandgap of less thanapproximately 0.5 eV.

In an embodiment, the nanocrystals of the third optically sensitivelayer are quantum confined to a bandgap corresponding to 490 nmwavelength.

In an embodiment, the nanocrystals of the third optically sensitivelayer are quantum confined to a bandgap of approximately 2.5 eV.

In an embodiment, the nanocrystals of the second optically sensitivelayer are quantum confined to a bandgap corresponding to 560 nmwavelength.

In an embodiment, nanocrystals of the second optically sensitive layerare quantum confined to a bandgap of approximately 2.2 eV.

In an embodiment, the nanocrystals of the first optically sensitivelayer are quantum confined to a bandgap of approximately 1.8 eV, or 1.2eV, or 0.9 eV, or 0.7 eV.

In an embodiment, the nanocrystals of the first optically sensitivelayer are quantum confined to a bandgap corresponding to 650, or 700, or800, or 900, or 1000, or 1300, or 1650 nm wavelength.

In an embodiment, the nanocrystals of the first optically sensitivelayer are quantum confined to a bandgap corresponding to 3 um or 5 umwavelength.

In an embodiment, the at least two optically sensitive layers includes athird optically sensitive layer and a fourth optically sensitive layer,wherein the third optically sensitive layer is over at least a portionof the second optically sensitive layer and the fourth opticallysensitive layer is over at least a portion of the third opticallysensitive layer.

In an embodiment, each of the optically sensitive layers comprisesnanocrystals of a material having a bulk bandgap of less than 0.5 eV,and wherein the nanocrystals in the first optically sensitive layer arequantum confined to have a bandgap corresponding to approximately 800 nmwavelength, the nanocrystals in the second optically sensitive layer arequantum confined to have a bandgap corresponding to approximately 630 nmwavelength, the nanocrystals in the third optically sensitive layer arequantum confined to have a bandgap corresponding to approximately 560 nmwavelength, and the nanocrystals in the fourth optically sensitive layerare quantum confined to have a bandgap corresponding to approximately490 nm wavelength.

In an embodiment, each of the optically sensitive layers comprisesnanocrystals of a material having a bulk bandgap of less thanapproximately 0.5 eV.

In an embodiment, the nanocrystals of the fourth optically sensitivelayer are quantum confined to a bandgap corresponding to 490 nmwavelength.

In an embodiment, the nanocrystals of the fourth optically sensitivelayer are quantum confined to a bandgap of approximately 2.5 eV.

In an embodiment, the nanocrystals of the third optically sensitivelayer are quantum confined to a bandgap corresponding to 560 nmwavelength.

In an embodiment, the nanocrystals of the third optically sensitivelayer are quantum confined to a bandgap of approximately 2.2 eV.

In an embodiment, the nanocrystals of the second optically sensitivelayer are quantum confined to a bandgap corresponding to 630, or 650, or670, or 700 nm wavelength.

In an embodiment, the nanocrystals of the second optically sensitivelayer are quantum confined to a bandgap of approximately 1.8 eV.

In an embodiment, the nanocrystals of the first optically sensitivelayer are quantum confined to a bandgap corresponding to 800, or 900, or1000, or 1300, or 1650 nm wavelength.

In an embodiment, the nanocrystals of the first optically sensitivelayer are quantum confined to a bandgap corresponding to 3 um or 5 umwavelength.

In an embodiment, the nanocrystals of the first optically sensitivelayer are quantum confined to a bandgap of approximately 1.2 eV, 0.9 eV,or 0.7 eV.

In an embodiment, each of the optically sensitive layers comprisesnanocrystals of the same material.

In an embodiment, at least one of the optically sensitive layerscomprises monodisperse nanocrystals.

In an embodiment, the nanocrystals are colloidal quantum dots.

In an embodiment, the quantum dots include a first carrier type and asecond carrier type, wherein the first carrier type is a flowing carrierand the second carrier type is one of a substantially blocked carrierand a trapped carrier.

In an embodiment, the colloidal quantum dots include organic ligands,wherein a flow of at least one of the first carrier type and the secondcarrier type is related to the organic ligands.

In an embodiment, each of the optically sensitive layers comprisesnanocrystals of different materials, wherein the first opticallysensitive layer includes a first material having a first bulk bandgapand the second optically sensitive layer includes a second materialhaving a second bulk bandgap.

In an embodiment, the first material comprises nanoparticles having afirst diameter and the second material comprises nanoparticles having asecond diameter.

In an embodiment, the first diameter is greater than or less than thesecond diameter.

In an embodiment, the first bulk bandgap is higher than the second bulkbandgap.

In an embodiment, the first optically sensitive layer comprises acomposition including lead sulfide (PbS), or lead selenide (PbSe), orlead tellurium (PbTe), or indium phosphide (InP), or indium arsenide(InAs), or germanium (Ge).

In an embodiment, the second optically sensitive layer comprises acomposition including indium sulfide (In₂S₃), or indium selenide(In₂Se₃), or indium tellurium (In₂Te₃), or bismuth sulfide (Bi₂S₃), orbismuth selenide (Bi₂Se₃), or bismuth tellurium (Bi₂Te₃), or indiumphosphide (InP), or silicon (Si), or germanium (Ge), or gallium arsenide(GaAs).

In an embodiment, the first optically sensitive layer comprises a firstcomposition including one of lead sulfide (PbS), lead selenide (PbSe),lead tellurium sulfide (PbTe), indium phosphide (InP), indium arsenide(InAs), and germanium (Ge), and the second optically sensitive layercomprises a second composition including one of indium sulfide (In₂S₃),indium selenide (In₂Se₃), indium tellurium (In₂Te₃), bismuth sulfide(Bi₂S₃), bismuth selenide (Bi₂Se₃), bismuth tellurium (Bi₂Te₃), indiumphosphide (InP), silicon (Si), and germanium (Ge).

In an embodiment, each of the optically sensitive layers comprisesdifferent compound semiconductor nanocrystals, wherein the firstoptically sensitive layer comprises a composition including lead and thesecond optically sensitive layer comprises a composition including oneof indium and bismuth.

In an embodiment, each of the optically sensitive layers comprisesdifferent compound semiconductor nanocrystals, wherein the secondoptically sensitive layer comprises a composition including cadmiumselenide (CdSe).

In an embodiment, the first optically sensitive layer comprises acomposition including lead sulfide (PbS), or lead selenide (PbSe), orindium phosphide (InP), or germanium (Ge).

In an embodiment, each of the optically sensitive layers comprisesdifferent compound semiconductor nanocrystals, wherein the firstoptically sensitive layer comprises a composition including one of leadsulfide (PbS), lead selenide (PbSe), indium phosphide (InP), andgermanium (Ge), wherein the second optically sensitive layer comprises acomposition including cadmium selenide (CdSe).

In an embodiment, each of the optically sensitive layers comprisesnanocrystals of a different particle size.

In an embodiment, nanocrystal particles of the first optically sensitivelayer are larger than nanocrystal particles of the second opticallysensitive layer.

In an embodiment, nanocrystal particles of the first optically sensitivelayer are smaller than nanocrystal particles of the second opticallysensitive layer.

In an embodiment, a first bulk bandgap of the first optically sensitivelayer is higher than a second bulk bandgap of the second opticallysensitive layer.

In an embodiment, a first increase in bandgap due to quantum confinementin the first optically sensitive layer is greater than a second increasein bandgap due to quantum confinement in the second optically sensitivelayer.

In an embodiment, the first optically sensitive layer comprises acomposition including lead sulfide (PbS), or lead selenide (PbSe), ortellurium sulfide (TeS), or indium phosphide (InP), or indium arsenide(InAs), or germanium (Ge).

In an embodiment, the second optically sensitive layer comprises acomposition including indium sulfide (In₂S₃), or indium selenide(In₂Se₃), or indium tellurium (In₂Te₃), or bismuth sulfide (Bi₂S₃), orbismuth selenide (Bi₂Se₃), or bismuth tellurium (Bi₂Te₃), or indiumphosphide (InP), or silicon (Si), or germanium (Ge), or gallium arsenide(GaAs).

In an embodiment, the first optically sensitive layer comprises a firstcomposition including one of lead sulfide (PbS), lead selenide (PbSe),lead tellurium sulfide (PbTe), indium phosphide (InP), indium arsenide(InAs), and germanium (Ge), and the second optically sensitive layercomprises a second composition including one of indium sulfide (In₂₅₃),indium selenide (In₂Se₃), indium tellurium (In₂Te₃), bismuth sulfide(Bi₂S₃), bismuth selenide (Bi₂Se₃), bismuth tellurium (Bi₂Te₃), indiumphosphide (InP), silicon (Si), and germanium (Ge).

In an embodiment, the second optically sensitive layer comprises ananocrystal material having an absorption onset at approximately 490 nmwavelength and the first optically sensitive layer comprises ananocrystal material having an absorption onset of less thanapproximately 560 nm wavelength, wherein a local absorption maximum isabsent from an absorption spectrum of at least one of the firstoptically sensitive layer and the second optically sensitive layer.

In an embodiment, the second optically sensitive layer comprises ananocrystal material absorptive to at least visible blue light andtransmissive to visible red light, and the first optically sensitivelayer comprises a nanocrystal material absorptive to at least visiblered light, visible green light and visible blue light.

In an embodiment, the at least two optically sensitive layers includes athird optically sensitive layer, wherein the third optically sensitivelayer is over at least a portion of the second optically sensitivelayer, wherein a local absorption maximum is absent from an absorptionspectrum of at least one of the first optically sensitive layer, thesecond optically sensitive layer, and the third optically sensitivelayer.

In an embodiment, the third optically sensitive layer comprises ananocrystal material having an absorption onset at approximately 490 nmwavelength and the second optically sensitive layer comprises ananocrystal material having an absorption onset of less thanapproximately 560 nm wavelength.

In an embodiment, the first optically sensitive layer comprises ananocrystal material having an absorption onset at approximately 650, or700, or 750, or 800, or 900, or 1000, or 1300, or 1650 nm wavelength.

In an embodiment, the first optically sensitive layer comprises ananocrystal material having an absorption onset at approximately 3 um or5 um wavelength.

In an embodiment, the third optically sensitive layer comprises ananocrystal material absorptive to at least visible blue light andtransmissive to visible green light, visible red light, and infraredlight, the second optically sensitive layer comprises a nanocrystalmaterial absorptive to at least visible blue light and visible greenlight and transmissive to visible red light and infrared light, and thefirst optically sensitive layer comprises a nanocrystal materialabsorptive to at least visible blue light, visible green light, andvisible red light.

In an embodiment, the first optically sensitive layer is absorptive toinfrared light. The embodiment further comprising a fourth opticallysensitive layer over at least a portion of the third optically sensitivelayer

In an embodiment, a local absorption maximum is absent from anabsorption spectrum of at least one of the first optically sensitivelayer, the second optically sensitive layer, the third opticallysensitive layer, and the fourth optically sensitive layer.

In an embodiment, the fourth optically sensitive layer comprises ananocrystal material having an absorption onset at approximately 490 nmwavelength.

In an embodiment, the third optically sensitive layer comprises ananocrystal material having an absorption onset of less thanapproximately 560 nm wavelength.

In an embodiment, the second optically sensitive layer comprises ananocrystal material having an absorption onset at approximately 630 nm,or 650 nm, or 670, or 700 nm wavelength.

In an embodiment, the first optically sensitive layer comprises ananocrystal material having an absorption onset at approximately 800 nm,or 900 nm, or 1000 nm, or 1300, or 1650 nm wavelength.

In an embodiment, the first optically sensitive layer comprises ananocrystal material having an absorption onset at approximately 3 um or5 um wavelength.

In an embodiment, the fourth optically sensitive layer comprises ananocrystal material absorptive to at least visible blue light andtransmissive to visible green light, visible red light, and infraredlight.

In an embodiment, the third optically sensitive layer comprises ananocrystal material absorptive to at least visible blue light andvisible green light and transmissive to visible red light and infraredlight.

In an embodiment, the second optically sensitive layer comprises ananocrystal material absorptive to at least visible blue light, visiblegreen light, and visible red light.

In an embodiment, the first optically sensitive layer comprises ananocrystal material absorptive to at least visible blue light, visiblegreen light, visible red light and infrared light.

In an embodiment, a third optically sensitive layer, the third opticallysensitive layer comprising a doped silicon region on a substrate of theintegrated circuit, the third optically sensitive layer positioned belowthe first optically sensitive layer and the second optically sensitivelayer.

In an embodiment, a third optically sensitive layer, the third opticallysensitive layer comprising a doped silicon region integrated with asubstrate of the integrated circuit, the third optically sensitive layerpositioned below the first optically sensitive layer and the secondoptically sensitive layer.

In an embodiment, a rate of the current flow through an opticallysensitive material of at least one optically sensitive layer has anon-linear relationship with intensity of the light absorbed by theoptically sensitive material.

In an embodiment, gain of an optically sensitive material of at leastone optically sensitive layer has a non-linear relationship withintensity of the light absorbed by the optically sensitive material.

Embodiments are directed to a photodetector wherein the bias comprises:

biasing the optically sensitive layers to operate as a current sinkduring a first period of time; and biasing the optically sensitivematerial to operate as a current source during a second period of time.

In an embodiment, the first period of time is an integration periodduring which a voltage is established based on the current flow throughthe optically sensitive material.

In an embodiment, the second period of time is a period of time duringwhich a reset is applied to the optically sensitive material, the resetincluding resetting a voltage difference across the optically sensitivematerial.

In an embodiment, the optically sensitive layers comprise anon-rectifying optically sensitive device.

In an embodiment, the integrated circuit comprises for each pixel regiona charge store and an integration circuit to establish a voltage basedon intensity of light absorbed by the optically sensitive layers over anintegration period of time.

In an embodiment, the integrated circuit includes at least onetransistor in electrical communication with the respective firstelectrode, wherein the charge store comprises parasitic capacitance ofthe at least one transistor.

In an embodiment, the integrated circuit includes a source followertransistor having a gate in electrical communication with the respectivefirst electrode.

In an embodiment, the parasitic capacitance comprises a parasiticcapacitance between the gate and a source of the source followertransistor.

In an embodiment, the integrated circuit includes a reset transistorhaving a gate in electrical communication with the respective firstelectrode.

In an embodiment, the parasitic capacitance comprises a parasiticcapacitance between a source and structures of a substrate of the resettransistor.

In an embodiment, the parasitic capacitance comprises metal-to-metalparasitic capacitance between nodes of the pixel circuit.

In an embodiment, the parasitic capacitance comprises metal-to-substrateparasitic capacitance between the charge store node and a siliconsubstrate.

In an embodiment, the parasitic capacitance is approximately in a rangeof 0.5 to 3 Femto Farads, or approximately in a range of 1 to 2 FemtoFarads.

In an embodiment, charge stored at the charge store is discharged by aflow of current through the optically sensitive layers during theintegration period of time.

In an embodiment, the photodetector comprises at least one color filter.It also comprises conversion circuitry.

In an embodiment, the integrated circuit includes the conversioncircuitry, the conversion circuitry located under the at least twooptically sensitive layers.

In an embodiment, the conversion circuitry is coupled to the integratedcircuit.

In an embodiment, the conversion circuitry converts the signals from afirst type to a second type.

In an embodiment, the conversion circuitry converts the signals fromanalog signals to digital signals.

In an embodiment, the conversion circuitry converts the signals fromdigital signals to analog signals.

In an embodiment, the photodetector further comprises compensationcircuitry.

In an embodiment, the compensation circuitry is coupled to theintegrated circuit.

In an embodiment, the integrated circuit includes the compensationcircuitry, the compensation circuitry located under the at least twooptically sensitive layers.

In an embodiment, the compensation circuitry adjusts the signal tocompensate for different properties among the optically sensitivelayers.

In an embodiment, the compensation circuitry at least partiallycompensates for nonlinearity of signals output from the opticallysensitive layers.

In an embodiment, the compensation circuitry at least partiallylinearizes digital data derived from the signals.

In an embodiment, the compensation circuitry at least partiallylinearizes the signals using a polynomial function.

In an embodiment, the compensation circuitry at least partiallylinearizes the signals using piecewise linear inversion of arelationship between intensity of the light and electrical properties ofat least one optically sensitive layer.

In an embodiment, the compensation circuitry at least partiallycompensates for variance in a rate of current flow in at least oneoptically sensitive layer over an integration period for a constantintensity of light.

In an embodiment, the compensation circuitry at least partiallycompensates for variance in a rate of current flow in at least oneoptically sensitive layer over an integration period for differingintensities of light.

In an embodiment, the compensation circuitry at least partiallycompensates for variance in gain in at least one optically sensitivelayer over an integration period for a constant intensity of light.

In an embodiment, the compensation circuitry at least partiallycompensates for variance in gain in at least one optically sensitivelayer over an integration period for differing intensities of light.

In an embodiment, the compensation circuitry: at least partiallycompensates for nonlinearity of signals output from the opticallysensitive layers; and at least partially compensates for a differencebetween dark currents of signals output from the optically sensitivelayers. The compensation circuitry includes a read out circuit anddemosaicing algorithm that outputs a corrected color matrix based onanalog quantities read out from the respective optically sensitivelayers.

In an embodiment, the corrected color matrix includes a red, green, blue(RGB) matrix.

In an embodiment, the compensation circuitry compensates fortransmission leakage between layers.

In an embodiment, the compensation circuitry includes image circuitry togenerate image data.

In an embodiment, the first optically sensitive layer comprises ananocrystal material having first photoconductive gain and the secondoptically sensitive layer comprises a nanocrystal material having asecond photoconductive gain, the image circuitry compensating for adifference between the first photoconductive gain and the secondphotoconductive gain.

In an embodiment, the compensation circuitry applies black levelcorrection that compensates for a difference between dark currents amongthe at least two optically sensitive layers by applying a plurality ofdark current compensations to the signal.

In an embodiment, the compensation circuitry applies a first darkcurrent compensation to a first signal from the first opticallysensitive layer and a second dark current compensation to a secondsignal from the second optically sensitive layer.

In an embodiment, the first dark current compensation is different fromthe second dark current compensation. The photodetector comprises atleast one black pixel. The at least one black pixel comprises at leasttwo optically sensitive opaque layers, a first optically sensitiveopaque layer and a second optically sensitive opaque layer, the firstoptically sensitive opaque layer and the second optically sensitiveopaque layer each comprising an optically sensitive layer covered withan opaque material, the first optically sensitive opaque layer over atleast a portion of a black pixel integrated circuit and the secondoptically sensitive opaque layer over the first optically sensitiveopaque layer, wherein each optically sensitive opaque layer isinterposed between a respective first electrode of the black pixel and arespective second electrode of the black pixel, wherein the integratedcircuit selectively applies a bias to the respective first and secondelectrodes of the black pixel and reads a dark current signal from theoptically sensitive opaque layers, wherein the dark current signal isrelated to the number of photons received by the respective opticallysensitive opaque layer.

In an embodiment, the black pixel generates a dark current.

In an embodiment, the dark current density is approximately in a rangeof 10 nanoamps (nA)/square centimeter (cm) to 500 nA/square cm.

In an embodiment, the dark current compensations include subtracting thedark current from the signals of the optically sensitive layers indifferent proportions.

In an embodiment, the dark current compensations include subtracting afirst portion of the dark current from a first signal of the secondoptically sensitive layer and subtracting a second portion of the darkcurrent from a second signal of the second optically sensitive layer.

In an embodiment, the first portion is larger than the second portion.

In an embodiment, the at least one black pixel comprises a first blackpixel corresponding to the first optically sensitive layer and a secondblack pixel corresponding to the second optically sensitive layer.

In an embodiment, the first black pixel generates a first dark currentand the second black pixel that generates a second dark current.

In an embodiment, the dark current compensation includes subtracting thefirst dark current from a first signal of the first optically sensitivelayer and subtracting the second dark current from a second signal ofthe second optically sensitive layer.

In an embodiment, the at least one black pixel comprises a plurality ofblack pixels generating a plurality of dark currents, wherein thecompensation circuitry generates the plurality of dark currentcompensations from the plurality of dark currents.

In an embodiment, responsivities of each of the optically sensitivelayers are approximately equal when a thickness of the second opticallysensitive layer is less than a thickness of the first opticallysensitive layer.

In an embodiment, a photodetector comprises bandgap reference circuitry,the bandgap reference circuitry at least one of integrated in theintegrated circuit and coupled to the integrated circuit.

In an embodiment, the black level correction is based on temperaturemonitoring by tracking a voltage from the bandgap reference circuitry.

In an embodiment, a fill factor is at least 80 percent, wherein the fillfactor is a ratio of absorbing area of each photodetector to a totalarea of the photodetector.

In an embodiment, the fill factor is approximately in a range of 80percent to 100 percent.

In an embodiment, the respective second electrode for the firstoptically sensitive layer and the second optically sensitive layercomprises a mesh between at least two adjacent photodetectors of theplurality of photodetectors.

In an embodiment, each photodetector comprises the first respectiveelectrode, wherein the respective second electrode for the firstoptically sensitive layer and the second optically sensitive layer ofeach photodetector of the plurality of photodetectors comprises a commonelectrode disposed around the respective first electrode, wherein thecommon electrode forms a mesh interposed between the plurality ofphotodetectors and is a common electrode for each optically sensitivelayer in the plurality of photodetectors.

What is claimed is:
 1. A photodetector comprising: an integratedcircuit; a plurality of optically sensitive layers; wherein a firstoptically sensitive layer is over at least a portion of the integratedcircuit; wherein a second optically sensitive layer is over at least aportion of the first optically sensitive layer; and wherein a thirdoptically sensitive layer is over at least a portion of the secondoptically sensitive layer, a thickness of the third optically sensitivelayer is less than a thickness of at least one of the first opticallysensitive layer and the second optically sensitive layer, a third darkcurrent of the third optically sensitive layer is less than a seconddark current of the second optically sensitive layer; wherein theoptically sensitive layers are interposed between two electrodes, theelectrodes including a respective first electrode and a respectivesecond electrode.
 2. The photodetector of claim 1, wherein theintegrated circuit selectively applies a bias to the electrodes andreads signals from the optically sensitive layers, wherein the signal isrelated to the number of photons received by the respective opticallysensitive layers.
 3. The photodetector of claim 1, wherein a thicknessof the third optically sensitive layer is greater than a thickness of atleast one of the first optically sensitive layer and the secondoptically sensitive layer.
 4. The photodetector of claim 1, wherein athickness of the second optically sensitive layer is less than athickness of the first optically sensitive layer.
 5. The photodetectorof claim 1, wherein the third optically sensitive layer is relativelycompletely absorbent of light in a first wavelength interval andrelatively completely transmissive of light outside the first wavelengthinterval.
 6. The photodetector of claim 5, wherein the second opticallysensitive layer is relatively completely absorbent of light in a secondwavelength interval and relatively completely transmissive of lightoutside the second wavelength interval, wherein the second wavelengthinterval includes and is larger than the first wavelength interval. 7.The photodetector of claim 6, wherein the first optically sensitivelayer is relatively completely absorbent of light in a third wavelengthinterval, wherein the third wavelength interval includes and is largerthan the second wavelength interval.
 8. The photodetector of claim 1,wherein at least one of the optically sensitive layers comprisesnanocrystals of a material having a bulk bandgap, and wherein thenanocrystals are quantum confined to have an effective bandgap more thantwice the bulk bandgap.
 9. The photodetector of claim 1, wherein atleast one of the optically sensitive layers includes nanocrystalscomprising nanoparticles, wherein a nanoparticle diameter of thenanoparticles is less than a Bohr exciton radius of bound electron-holepairs within the nanoparticle.
 10. The photodetector of claim 1, whereina first diameter of nanocrystals of the first optically sensitive layeris greater than a second diameter of nanocrystals of the secondoptically sensitive layer.
 11. The photodetector of claim 1, wherein afirst diameter of nanocrystals of the first optically sensitive layer isless than a second diameter of nanocrystals of the second opticallysensitive layer.
 12. The photodetector of claim 1, wherein at least oneof the optically sensitive layers comprises nanocrystals of a materialhaving a bulk bandgap of less than approximately 0.5 electronvolts (eV),and wherein the nanocrystals are quantum confined to have a bandgap morethan 1.0 eV.
 13. The photodetector of claim 1, wherein each of theoptically sensitive layers comprises nanocrystals of a material having abulk bandgap of less than 0.5 eV, and wherein the nanocrystals in thefirst optically sensitive layer are quantum confined to have a bandgapof approximately 1.8 eV, the nanocrystals in the second opticallysensitive layer are quantum confined to have a bandgap of approximately2.2 eV, and the nanocrystals in the third optically sensitive layer arequantum confined to have a bandgap of more than approximately 2.5 eV.14. The photodetector of claim 1, wherein each of the opticallysensitive layers comprises nanocrystals of a material having a bulkbandgap of less than approximately 0.5 eV.
 15. The photodetector ofclaim 14, wherein the nanocrystals of the third optically sensitivelayer are quantum confined to a bandgap corresponding to 490 nmwavelength.
 16. The photodetector of claim 14, wherein the nanocrystalsof the third optically sensitive layer are quantum confined to a bandgapof approximately 2.5 eV.
 17. The photodetector of claim 14, wherein thenanocrystals of the second optically sensitive layer are quantumconfined to a bandgap corresponding to 560 nm wavelength.
 18. Thephotodetector of claim 14, wherein the nanocrystals of the secondoptically sensitive layer are quantum confined to a bandgap ofapproximately 2.2 eV.
 19. The photodetector of claim 14, wherein thenanocrystals of the first optically sensitive layer are quantum confinedto a bandgap of approximately 1.8 eV.
 20. The photodetector of claim 14,wherein the nanocrystals of the first optically sensitive layer arequantum confined to a bandgap of approximately 1.2 eV.
 21. Thephotodetector of claim 14, wherein the nanocrystals of the firstoptically sensitive layer are quantum confined to a bandgap ofapproximately 0.9 eV.
 22. The photodetector of claim 14, wherein thenanocrystals of the first optically sensitive layer are quantum confinedto a bandgap of approximately 0.7 eV.
 23. The photodetector of claim 14,wherein the nanocrystals of the first optically sensitive layer arequantum confined to a bandgap corresponding to 650 nm wavelength. 24.The photodetector of claim 14, wherein the nanocrystals of the firstoptically sensitive layer are quantum confined to a bandgapcorresponding to 700 nm wavelength.
 25. The photodetector of claim 1,further comprising a fourth optically sensitive layer, wherein thefourth optically sensitive layer is over at least a portion of the thirdoptically sensitive layer.
 26. The photodetector of claim 25, whereineach of the optically sensitive layers comprises nanocrystals of amaterial having a bulk bandgap of less than approximately 0.5 eV. 27.The photodetector of claim 26, wherein the nanocrystals of the fourthoptically sensitive layer are quantum confined to a bandgapcorresponding to 490 nm wavelength.
 28. The photodetector of claim 26,wherein the nanocrystals of the fourth optically sensitive layer arequantum confined to a bandgap of approximately 2.5 eV.
 29. Thephotodetector of claim 26, wherein the nanocrystals of the thirdoptically sensitive layer are quantum confined to a bandgapcorresponding to 560 nm wavelength.
 30. The photodetector of claim 26,wherein the nanocrystals of the third optically sensitive layer arequantum confined to a bandgap of approximately 2.2 eV.
 31. Thephotodetector of claim 26, wherein the nanocrystals of the secondoptically sensitive layer are quantum confined to a bandgapcorresponding to 630 nm wavelength.
 32. The photodetector of claim 26,wherein the nanocrystals of the second optically sensitive layer arequantum confined to a bandgap corresponding to 650 nm wavelength. 33.The photodetector of claim 26, wherein the nanocrystals of the secondoptically sensitive layer are quantum confined to a bandgapcorresponding to 670 nm wavelength.
 34. The photodetector of claim 26,wherein the nanocrystals of the second optically sensitive layer arequantum confined to a bandgap corresponding to 700 nm wavelength. 35.The photodetector of claim 26, wherein the nanocrystals of the secondoptically sensitive layer are quantum confined to a bandgap ofapproximately 1.8 eV.
 36. The photodetector of claim 26, wherein thenanocrystals of the first optically sensitive layer are quantum confinedto a bandgap corresponding to 800 nm wavelength.
 37. The photodetectorof claim 26, wherein the nanocrystals of the first optically sensitivelayer are quantum confined to a bandgap corresponding to 900 nmwavelength.
 38. The photodetector of claim 26, wherein the nanocrystalsof the first optically sensitive layer are quantum confined to a bandgapcorresponding to 1000 nm wavelength.
 39. The photodetector of claim 26,wherein the nanocrystals of the first optically sensitive layer arequantum confined to a bandgap corresponding to 1300 nm wavelength. 40.The photodetector of claim 26, wherein the nanocrystals of the firstoptically sensitive layer are quantum confined to a bandgapcorresponding to 1650 nm wavelength.
 41. The photodetector of claim 26,wherein the nanocrystals of the first optically sensitive layer arequantum confined to a bandgap corresponding to 3 um wavelength.
 42. Thephotodetector of claim 26, wherein the nanocrystals of the firstoptically sensitive layer are quantum confined to a bandgapcorresponding to 5 um wavelength.
 43. The photodetector of claim 26,wherein the nanocrystals of the first optically sensitive layer arequantum confined to a bandgap of approximately 1.2 eV.
 44. Thephotodetector of claim 26, wherein the nanocrystals of the firstoptically sensitive layer are quantum confined to a bandgap ofapproximately 0.9 eV.
 45. The photodetector of claim 26, wherein thenanocrystals of the first optically sensitive layer are quantum confinedto a bandgap of approximately 0.7 eV.
 46. The photodetector of claim 1,further comprising a fourth optically sensitive layer over at least aportion of the third optically sensitive layer.
 47. The photodetector ofclaim 46, wherein the third optically sensitive layer comprises ananocrystal material absorptive to at least visible blue light andvisible green light and transmissive to visible red light and infraredlight.
 48. The photodetector of claim 46, wherein the second opticallysensitive layer comprises a nanocrystal material absorptive to at leastvisible blue light, visible green light, and visible red light.
 49. Thephotodetector of claim 46, wherein the first optically sensitive layercomprises a nanocrystal material absorptive to at least visible bluelight, visible green light, visible red light and infrared light.
 50. Aphotodetector comprising: an integrated circuit; a plurality ofoptically sensitive layers; wherein a first optically sensitive layer isover at least a portion of the integrated circuit; wherein a secondoptically sensitive layer is over at least a portion of the firstoptically sensitive layer; and wherein a third optically sensitive layeris over at least a portion of the second optically sensitive layer, athickness of the third optically sensitive layer being less than athickness of at least one of the first optically sensitive layer and thesecond optically sensitive layer; wherein the optically sensitive layersare interposed between two electrodes, the electrodes including arespective first electrode and a respective second electrode, the atleast two optically sensitive layers including a fourth opticallysensitive layer, wherein the fourth optically sensitive layer is over atleast a portion of the third optically sensitive layer, wherein athickness of the fourth optically sensitive layer is less than athickness of one of the first optically sensitive layer, the secondoptically sensitive layer, and the third optically sensitive layer. 51.The photodetector of claim 50, wherein a thickness of the fourthoptically sensitive layer is less than a thickness of the thirdoptically sensitive layer.
 52. The photodetector of claim 51, wherein athickness of the third optically sensitive layer is less than athickness of the second optically sensitive layer.
 53. The photodetectorof claim 52, wherein a thickness of the second optically sensitive layeris less than a thickness of the first optically sensitive layer.
 54. Thephotodetector of claim 50, wherein the fourth optically sensitive layeris relatively completely absorbent of light in a first wavelengthinterval and relatively completely transmissive of light outside thefirst wavelength interval.
 55. The photodetector of claim 54, whereinthe third optically sensitive layer is relatively completely absorbentof light in a third wavelength interval and relatively completelytransmissive of light outside the third wavelength interval, wherein thethird wavelength interval includes and is larger than the fourthwavelength interval.
 56. The photodetector of claim 55, wherein thesecond optically sensitive layer is relatively completely absorbent oflight in a second wavelength interval, wherein the second wavelengthinterval includes and is larger than the third wavelength interval. 57.The photodetector of claim 56, wherein the first optically sensitivelayer is relatively completely absorbent of light in a first wavelengthinterval, wherein the first wavelength interval includes and is largerthan the second wavelength interval.
 58. The photodetector of claim 50,wherein a fourth dark current of the fourth optically sensitive layer isless than at least one of a third dark current of the third opticallysensitive layer, a second dark current of the second optically sensitivelayer, and a first dark current of the first optically sensitive layer.59. The photodetector of claim 50, wherein a third dark current of thethird optically sensitive layer is less than at least one of a fourthdark current of the fourth optically sensitive layer, a second darkcurrent of the second optically sensitive layer, and a first darkcurrent of the first optically sensitive layer.
 60. The photodetector ofclaim 50, wherein a second dark current of the second opticallysensitive layer is less than at least one of a fourth dark current ofthe fourth optically sensitive layer, a third dark current of the thirdoptically sensitive layer, and a first dark current of the firstoptically sensitive layer.
 61. The photodetector of claim 50, wherein afirst dark current of the first optically sensitive layer is less thanat least one of a fourth dark current of the fourth optically sensitivelayer, a third dark current of the third optically sensitive layer, anda second dark current of the second optically sensitive layer.
 62. Aphotodetector comprising: an integrated circuit; a plurality ofoptically sensitive layers; wherein a first optically sensitive layer isover at least a portion of the integrated circuit; wherein a secondoptically sensitive layer is over at least a portion of the firstoptically sensitive layer; and wherein a third optically sensitive layeris over at least a portion of the second optically sensitive layer, atleast one of the optically sensitive layers comprises a nanocrystalmaterial having photoconductive gain and a responsivity of at leastapproximately 0.4 amps/volt (A/V); wherein the optically sensitivelayers are interposed between two electrodes, the electrodes including arespective first electrode and a respective second electrode.
 63. Thephotodetector of claim 62, wherein the responsivity is achieved when abias is applied between the respective first electrode and therespective second electrode, wherein the bias is approximately in arange of 1 volt to 5 volts.
 64. The photodetector of claim 63, whereinthe bias is approximately 0.5 volts.
 65. The photodetector of claim 63,wherein the bias is approximately 1 volt.
 66. The photodetector of claim63, wherein the bias is approximately 1.2 volts.
 67. The photodetectorof claim 63, wherein the bias is approximately 1.5 volts.
 68. Aphotodetector comprising: an integrated circuit; a plurality ofoptically sensitive layers; wherein a first optically sensitive layer isover at least a portion of the integrated circuit; wherein a secondoptically sensitive layer is over at least a portion of the firstoptically sensitive layer; and wherein a third optically sensitive layeris over at least a portion of the second optically sensitive layer;wherein the optically sensitive layers are interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode, the third optically sensitive layercomprises a nanocrystal material absorptive to at least visible bluelight and transmissive to visible green light, visible red light, andinfrared light, the second optically sensitive layer comprises ananocrystal material absorptive to at least visible blue light andvisible green light and transmissive to visible red light and infraredlight, and the first optically sensitive layer comprises a nanocrystalmaterial absorptive to at least visible blue light, visible green light,and visible red light.
 69. The photodetector of claim 68, wherein thefirst optically sensitive layer is absorptive to infrared light.
 70. Aphotodetector comprising: an integrated circuit; a plurality ofoptically sensitive layers; wherein a first optically sensitive layer isover at least a portion of the integrated circuit; wherein a secondoptically sensitive layer is over at least a portion of the firstoptically sensitive layer; wherein a third optically sensitive layer isover at least a portion of the second optically sensitive layer; andwherein a fourth optically sensitive layer is over at least a portion ofthe third optically sensitive layer, the fourth optically sensitivelayer comprises a nanocrystal material having an absorption onset atapproximately 490 nm wavelength; wherein the optically sensitive layersare interposed between two electrodes, the electrodes including arespective first electrode and a respective second electrode.
 71. Thephotodetector of claim 70, wherein the third optically sensitive layercomprises a nanocrystal material having an absorption onset of less thanapproximately 560 nm wavelength.
 72. The photodetector of claim 71,wherein the second optically sensitive layer comprises a nanocrystalmaterial having an absorption onset at approximately 630 nm wavelength.73. The photodetector of claim 71, wherein the second opticallysensitive layer comprises a nanocrystal material having an absorptiononset at approximately 650 nm wavelength.
 74. The photodetector of claim71, wherein the second optically sensitive layer comprises a nanocrystalmaterial having an absorption onset at approximately 670 nm wavelength.75. The photodetector of claim 71, wherein the second opticallysensitive layer comprises a nanocrystal material having an absorptiononset at approximately 700 nm wavelength.
 76. The photodetector of claim71, wherein the first optically sensitive layer comprises a nanocrystalmaterial having an absorption onset at approximately 800 nm wavelength.77. The photodetector of claim 71, wherein the first optically sensitivelayer comprises a nanocrystal material having an absorption onset atapproximately 900 nm wavelength.
 78. The photodetector of claim 71,wherein the first optically sensitive layer comprises a nanocrystalmaterial having an absorption onset at approximately 1000 nm wavelength.79. The photodetector of claim 71, wherein the first optically sensitivelayer comprises a nanocrystal material having an absorption onset atapproximately 1300 nm wavelength.
 80. The photodetector of claim 71,wherein the first optically sensitive layer comprises a nanocrystalmaterial having an absorption onset at approximately 1650 nm wavelength.81. The photodetector of claim 71, wherein the first optically sensitivelayer comprises a nanocrystal material having an absorption onset atapproximately 3 um wavelength.
 82. The photodetector of claim 71,wherein the first optically sensitive layer comprises a nanocrystalmaterial having an absorption onset at approximately 5 um wavelength.83. A photodetector comprising: an integrated circuit; a plurality ofoptically sensitive layers; wherein a first optically sensitive layer isover at least a portion of the integrated circuit; wherein a secondoptically sensitive layer is over at least a portion of the firstoptically sensitive layer; and wherein a third optically sensitive layeris over at least a portion of the second optically sensitive layer, athickness of the third optically sensitive layer being less than athickness of at least one of the first optically sensitive layer and thesecond optically sensitive layer, a third dark current of the thirdoptically sensitive layer being less than a first dark current of thefirst optically sensitive layer; wherein the optically sensitive layersare interposed between two electrodes, the electrodes including arespective first electrode and a respective second electrode.
 84. Aphotodetector comprising: an integrated circuit; a plurality ofoptically sensitive layers; wherein a first optically sensitive layer isover at least a portion of the integrated circuit; wherein a secondoptically sensitive layer is over at least a portion of the firstoptically sensitive layer; and wherein a third optically sensitive layeris over at least a portion of the second optically sensitive layer, athickness of the third optically sensitive layer being less than athickness of at least one of the first optically sensitive layer and thesecond optically sensitive layer, a second dark current of the secondoptically sensitive layer being less than a first dark current of thefirst optically sensitive layer; wherein the optically sensitive layersare interposed between two electrodes, the electrodes including arespective first electrode and a respective second electrode.
 85. Aphotodetector comprising: an integrated circuit; a plurality ofoptically sensitive layers; wherein a first optically sensitive layer isover at least a portion of the integrated circuit; wherein a secondoptically sensitive layer is over at least a portion of the firstoptically sensitive layer; and wherein a third optically sensitive layeris over at least a portion of the second optically sensitive layer;wherein the optically sensitive layers are interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode, each of the optically sensitive layerscomprises nanocrystals of a material having a bulk bandgap of less thanapproximately 0.5 eV, the nanocrystals of the first optically sensitivelayer being quantum confined to a bandgap corresponding to an 800 nmwavelength.
 86. A photodetector comprising: an integrated circuit; aplurality of optically sensitive layers; wherein a first opticallysensitive layer is over at least a portion of the integrated circuit;wherein a second optically sensitive layer is over at least a portion ofthe first optically sensitive layer; and wherein a third opticallysensitive layer is over at least a portion of the second opticallysensitive layer; wherein the optically sensitive layers are interposedbetween two electrodes, the electrodes including a respective firstelectrode and a respective second electrode, each of the opticallysensitive layers comprises nanocrystals of a material having a bulkbandgap of less than approximately 0.5 eV, the nanocrystals of the firstoptically sensitive layer being quantum confined to a bandgapcorresponding to a 900 nm wavelength.
 87. A photodetector comprising: anintegrated circuit; a plurality of optically sensitive layers; wherein afirst optically sensitive layer is over at least a portion of theintegrated circuit; wherein a second optically sensitive layer is overat least a portion of the first optically sensitive layer; and wherein athird optically sensitive layer is over at least a portion of the secondoptically sensitive layer; wherein the optically sensitive layers areinterposed between two electrodes, the electrodes including a respectivefirst electrode and a respective second electrode, each of the opticallysensitive layers comprises nanocrystals of a material having a bulkbandgap of less than approximately 0.5 eV, the nanocrystals of the firstoptically sensitive layer being quantum confined to a bandgapcorresponding to a 1000 nm wavelength.
 88. A photodetector comprising:an integrated circuit; a plurality of optically sensitive layers;wherein a first optically sensitive layer is over at least a portion ofthe integrated circuit; wherein a second optically sensitive layer isover at least a portion of the first optically sensitive layer; andwherein a third optically sensitive layer is over at least a portion ofthe second optically sensitive layer; wherein the optically sensitivelayers are interposed between two electrodes, the electrodes including arespective first electrode and a respective second electrode, each ofthe optically sensitive layers comprises nanocrystals of a materialhaving a bulk bandgap of less than approximately 0.5 eV, thenanocrystals of the first optically sensitive layer being quantumconfined to a bandgap corresponding to a 1300 nm wavelength.
 89. Aphotodetector comprising: an integrated circuit; a plurality ofoptically sensitive layers; wherein a first optically sensitive layer isover at least a portion of the integrated circuit; wherein a secondoptically sensitive layer is over at least a portion of the firstoptically sensitive layer; and wherein a third optically sensitive layeris over at least a portion of the second optically sensitive layer;wherein the optically sensitive layers are interposed between twoelectrodes, the electrodes including a respective first electrode and arespective second electrode, each of the optically sensitive layerscomprises nanocrystals of a material having a bulk bandgap of less thanapproximately 0.5 eV, the nanocrystals of the first optically sensitivelayer being quantum confined to a bandgap corresponding to a 1650 nmwavelength.
 90. A photodetector comprising: an integrated circuit; aplurality of optically sensitive layers; wherein a first opticallysensitive layer is over at least a portion of the integrated circuit;wherein a second optically sensitive layer is over at least a portion ofthe first optically sensitive layer; and wherein a third opticallysensitive layer is over at least a portion of the second opticallysensitive layer; wherein the optically sensitive layers are interposedbetween two electrodes, the electrodes including a respective firstelectrode and a respective second electrode, each of the opticallysensitive layers comprises nanocrystals of a material having a bulkbandgap of less than approximately 0.5 eV, the nanocrystals of the firstoptically sensitive layer being quantum confined to a bandgapcorresponding to a 3 μm wavelength.
 91. A photodetector comprising: anintegrated circuit; a plurality of optically sensitive layers; wherein afirst optically sensitive layer is over at least a portion of theintegrated circuit; wherein a second optically sensitive layer is overat least a portion of the first optically sensitive layer; and wherein athird optically sensitive layer is over at least a portion of the secondoptically sensitive layer; wherein the optically sensitive layers areinterposed between two electrodes, the electrodes including a respectivefirst electrode and a respective second electrode, each of the opticallysensitive layers comprises nanocrystals of a material having a bulkbandgap of less than approximately 0.5 eV, the nanocrystals of the firstoptically sensitive layer being quantum confined to a bandgapcorresponding to a 5 μm wavelength.
 92. A photodetector comprising: anintegrated circuit; a plurality of optically sensitive layers; wherein afirst optically sensitive layer is over at least a portion of theintegrated circuit; wherein a second optically sensitive layer is overat least a portion of the first optically sensitive layer; and wherein athird optically sensitive layer is over at least a portion of the secondoptically sensitive layer; wherein a fourth optically sensitive layer isover at least a portion of the third optically sensitive layer; whereinthe optically sensitive layers are interposed between two electrodes,the electrodes including a respective first electrode and a respectivesecond electrode, each of the optically sensitive layers comprisesnanocrystals of a material having a bulk bandgap of less than 0.5 eV,the nanocrystals in the first optically sensitive layer being quantumconfined to have a bandgap corresponding to approximately 800 nmwavelength, the nanocrystals in the second optically sensitive layerbeing quantum confined to have a bandgap corresponding to approximately630 nm wavelength, the nanocrystals in the third optically sensitivelayer being quantum confined to have a bandgap corresponding toapproximately 560 nm wavelength, and the nanocrystals in the fourthoptically sensitive layer being quantum confined to have a bandgapcorresponding to approximately 490 nm wavelength.
 93. A photodetectorcomprising: an integrated circuit; a plurality of optically sensitivelayers; wherein a first optically sensitive layer is over at least aportion of the integrated circuit; wherein a second optically sensitivelayer is over at least a portion of the first optically sensitive layer;wherein a third optically sensitive layer is over at least a portion ofthe second optically sensitive layer; and wherein a fourth opticallysensitive layer is over at least a portion of the third opticallysensitive layer; wherein a local absorption maximum is absent from anabsorption spectrum of at least one of the first optically sensitivelayer, the second optically sensitive layer, the third opticallysensitive layer, and the fourth optically sensitive layer; and whereinthe optically sensitive layers are interposed between two electrodes,the electrodes including a respective first electrode and a respectivesecond electrode.
 94. A photodetector comprising: an integrated circuit;a plurality of optically sensitive layers; wherein a first opticallysensitive layer is over at least a portion of the integrated circuit;wherein a second optically sensitive layer is over at least a portion ofthe first optically sensitive layer; wherein a third optically sensitivelayer is over at least a portion of the second optically sensitivelayer; and wherein a fourth optically sensitive layer is over at least aportion of the third optically sensitive layer, the fourth opticallysensitive layer comprises a nanocrystal material absorptive to at leastvisible blue light and transmissive to visible green light, visible redlight, and infrared light; wherein the optically sensitive layers areinterposed between two electrodes, the electrodes including a respectivefirst electrode and a respective second electrode.